Learn Hardcore Swedish: Innan gästerna kommer tänder hon alla lampor i vardagsrummet. - Before the guests arrive she turns on all the lights in the living room.

The finite verb (here: tänder) should be the second element in a main clause.
If you start the sentence with something other than the subject (here: the time clause Innan gästerna kommer), that whole part counts as the first element.
The verb then has to come next, and the subject comes after the verb.

So:

Innan gästerna kommer (1st element)
tänder (2nd element, the verb)
hon (3rd element, the subject)
alla lampor i vardagsrummet (rest of the sentence)

If you didn’t move the time clause to the front, the sentence would be:

Hon tänder alla lampor i vardagsrummet innan gästerna kommer.

Here, the subject hon is the first element, so tänder still comes second.

Why is it kommer (present tense) when the guests haven’t arrived yet? Shouldn’t it be a future tense?

Swedish often uses the present tense to talk about the near future, especially when there is a time expression or a time clause:

Innan gästerna kommer = before the guests arrive / before the guests come

Similarly:

Jag åker imorgon. = I’m leaving tomorrow.
Vi ses nästa vecka. = We’ll see each other next week.

You could say ska komma in some contexts, but in time clauses with innan, när, om, etc., Swedish strongly prefers the simple present even if it refers to the future:

Innan gästerna kommer is natural.
Innan gästerna ska komma usually sounds unnecessary or awkward.

What is the difference between innan and före, and why do we use innan here?

Both relate to the idea of before, but they are used differently:

innan = a subordinating conjunction; it introduces a clause (with a verb).
- Innan gästerna kommer (clause: the guests come)
före = usually a preposition; it is used before a noun or pronoun, not before a full clause.
- före gästerna (before the guests)
- före middagen (before dinner)

So you can say:

Innan gästerna kommer tänder hon … ✅
Hon tänder … före gästerna kommer. ❌ (ungrammatical in standard Swedish)
Hon tänder … före gästerna. ✅

If you really want a clause after före, you must use a longer structure like före det att gästerna kommer, but that sounds formal and is much less common than innan gästerna kommer.

Why is it gästerna and not just gäster or de gästerna?

Swedish marks definiteness on the noun itself with an ending:

en gäst = a guest
gästen = the guest
gäster = guests
gästerna = the guests

In your sentence, we are talking about specific guests that both speaker and listener can identify (for example, invited guests), so the definite plural is natural:

Innan gästerna kommer … = Before the guests arrive …

Why not de gästerna?

de gästerna usually means “those guests” (with extra emphasis or contrast).
- De gästerna du bjöd förra gången = those guests you invited last time

So:

gästerna = the guests (normal definiteness)
de gästerna = those (particular) guests (more specific/contrastive)

Why is it alla lampor, not alla lamporna or just lamporna?

You have a choice depending on whether you want the noun to be indefinite or definite:

alla lampor = all lamps (indefinite plural)
alla lamporna = all the lamps (definite plural)
lamporna = the lamps

In practice, both alla lampor and alla lamporna can be used here:

tänder hon alla lampor i vardagsrummet
tänder hon alla lamporna i vardagsrummet

The difference is subtle:

alla lamporna often implies all of a specific, known set of lamps in that room.
alla lampor can feel slightly more general, like “every lamp there is in the living room,” but in everyday speech many people would use either form with almost no difference in meaning.

If you just said:

Hon tänder lamporna i vardagsrummet.
= She turns on the lamps in the living room. (no emphasis on “all”)

Why is it i vardagsrummet and not just i vardagsrum?

vardagsrum is a neuter noun:

ett vardagsrum = a living room
vardagsrummet = the living room

Swedish normally marks definiteness when talking about a specific room that is understood from context (for example, “the living room (in the home we’re talking about)”):

i vardagsrummet = in the living room (specific, known room)

Saying i vardagsrum without the ending sounds incomplete or wrong in this context, similar to saying “in living room” without “the” or “a” in English.

How is vardagsrummet formed from vardagsrum?

You start with the base noun:

vardagsrum = living room

This is a neuter noun (it uses ett in the indefinite):

ett vardagsrum = a living room

To make it definite singular, you add -et, which merges phonetically with the final m:

vardagsrum
- -et → vardagsrummet
  = the living room

So the pattern is:

ett vardagsrum → vardagsrummet

Why is the word order gästerna kommer and not kommer gästerna in the first part?

That part is a subordinate clause introduced by innan:

Innan gästerna kommer …

In subordinate clauses, Swedish does not follow strict V2 order. Instead, the usual word order is:

subject – verb – (object/adverbials)

So we get:

gästerna (subject)
kommer (verb)

If you said innan kommer gästerna, it would sound wrong in standard Swedish. V2 (kommer gästerna) is for main clauses, for example:

Gästerna kommer snart. = The guests are arriving soon.
Snart kommer gästerna. = Soon the guests are arriving.

Could I put the time clause at the end and say: Hon tänder alla lampor i vardagsrummet innan gästerna kommer?

Yes, that’s completely correct and very natural:

Hon tänder alla lampor i vardagsrummet innan gästerna kommer.

The meaning is the same. The difference is just focus and style:

Starting with Innan gästerna kommer … gives extra emphasis to the time condition.
Ending with … innan gästerna kommer sounds a bit more neutral and is probably more common in everyday speech.

In both cases, the clause innan gästerna kommer has the same structure internally (subject before verb).

Why is there no comma after Innan gästerna kommer?

Modern Swedish comma rules are less strict than English ones. A comma can be used after a fronted subordinate clause, but in many cases it’s optional, especially if the clause is short and the sentence is easy to read.

So both of these are accepted:

Innan gästerna kommer tänder hon alla lampor …
Innan gästerna kommer, tänder hon alla lampor …

Stylistically:

Many writers today omit the comma unless it helps clarity.
Textbooks and older styles more often include the comma.

So the version without a comma is not wrong; it follows modern, lighter punctuation practice.

What exactly does tänder mean here, and how is it related to other forms?

Here, tänder is the present tense of the verb tända:

att tända = to light / to turn on (a light, a candle, etc.)
hon tänder = she lights / she turns on

Some useful forms:

Jag tände lampan. = I turned on the lamp. (past)
Kan du tända ljusen? = Can you light the candles? (infinitive)

Note that tänder can also be a noun meaning “teeth” (plural of tand), but in your sentence the grammar and context make it clear that it’s the verb.

How do you pronounce tänder, especially the ä?

Rough guide:

tänder ≈ [TEN-der], but with a Swedish ä.

Details:

tän-:
- t as in top
- ä is like the vowel in English “ten” or “cat”, but a bit clearer/purer.
- n as in no
-der:
- d as in do
- e like in “bed” (short)
- r often rolled or tapped

So: TÄN-der with main stress on the first syllable.

How do you pronounce vardagsrummet?

Very roughly: [VAR-dags-rum-met], but connected more smoothly.

Syllables and stresses:

VAR- = stressed syllable
-dags- = unstressed (often reduced when spoken quickly)
RUM- = secondary stress
-met = short, unstressed ending

Approximation:

var- like English “var” in “variable” (but slightly more open vowel, somewhere between “far” and “for” depending on accent)
-dags- like “dags” in “dag’s” but very reduced in fast speech
rum like English “room” but with a shorter vowel
-met like “met” in English

In everyday speech, it often sounds like VAR-das-rum-met (the g can be very soft or disappear).

Could I say innan gästerna ska komma to emphasize the future?

You can say innan gästerna ska komma, but:

It often sounds unnecessary or slightly awkward in neutral speech.
In most situations, Swedish speakers just use present tense after innan when referring to the future:
- Innan gästerna kommer tänder hon … (normal, natural)

You might use ska komma in special contexts, for example, when stressing an arrangement or plan:

Innan gästerna ska komma måste vi städa.
(More like: “Before the time when the guests are scheduled to come, we have to clean.”)

But even there, most people would still just say innan gästerna kommer.

Can innan also be used without a verb, like före can?

Normally, innan is used to introduce a clause with a verb:

innan gästerna kommer
innan vi äter
innan du går hem

före is used with nouns or pronouns:

före gästerna (before the guests)
före middagen (before dinner)
före honom (before him)

You will sometimes see innan used with just a time word in very informal speech (e.g. innan klockan åtta), but in standard grammar:

innan → before a clause
före → before a noun / pronoun / time expression