Um leið og við finnum sætin okkar, slekk ég á símanum.

Because Icelandic usually follows a verb-second word order in main clauses.

The sentence begins with the time clause Um leið og við finnum sætin okkar. After that whole clause comes the main clause, and in the main clause the finite verb must come first:

• Um leið og ... , slekk ég á símanum.

So the order is:

• introductory element
• verb
• subject

This is very common in Icelandic:

• Þegar ég kem heim, borða ég.
• Á morgun fer hann til Akureyrar.

If there were no introductory clause, you would say:

• Ég slekk á símanum.

Um leið og is a common expression meaning as soon as, once, or sometimes just as.

In this sentence, it introduces a time clause:

• Um leið og við finnum sætin okkar = as soon as we find our seats

A helpful way to think of it is as a fixed phrase rather than translating each word separately every time.

You will often see it with present tense when talking about future events:

• Um leið og hann kemur, förum við.
  • As soon as he comes, we leave.

So here it marks the moment after which the main action happens.

Icelandic often uses the present tense for actions in the future, especially when the future is understood from context.

So:

• við finnum
• slekk ég

can both describe what will happen next.

This is very similar to English in some time-clause patterns:

• As soon as we find our seats, I turn off my phone.
• More natural English would often be I’ll turn off my phone, but Icelandic commonly keeps the present tense.

So the grammar is normal Icelandic even if the English translation may use will.

In Icelandic, possessive words like okkar often come after the noun when the noun is definite.

So:

• sætin okkar = our seats

Here:

• sætin = the seats
• okkar = our

This structure is extremely common:

• bíllinn minn = my car
• húsið okkar = our house
• vinirnir hans = his friends

Putting okkar before the noun is generally not how this idea is expressed in ordinary Icelandic.

Sætin is the definite plural form of sæti (seat).

The noun sæti is neuter. Its plural indefinite form is also sæti, and the definite plural adds -n:

• sæti = seat / seats
• sætin = the seats

In this sentence, it is the direct object of finnum (find), so it is in the accusative plural. For this noun, the nominative and accusative plural look the same in the definite form:

• sætin

So learners often just need to recognize it as the seats.

Finnum is the 1st person plural present tense of finna (to find).

So:

• ég finn = I find
• þú finnur = you find
• hann/hún/það finnur = he/she/it finds
• við finnum = we find
• þið finnið = you find
• þeir/þær/þau finna = they find

Because the subject is við (we), the verb must be finnum.

Yes. Slekk is the 1st person singular present tense of slökkva (to switch off, turn off, extinguish).

This verb changes its stem:

• infinitive: slökkva
• ég slekk
• þú slekkur
• hann/hún/það slekkur
• við slökkvum

So the form may look surprising at first because it does not stay as slökk- in every form.

In this sentence:

• slekk ég = I turn off

This is because slökkva á is the normal Icelandic expression for turn off something like a phone, light, radio, etc.

So Icelandic says:

• slökkva á símanum = turn off the phone
• slökkva á ljósinu = turn off the light

The preposition á here takes the dative, which is why síminn becomes símanum.

So:

• sími = a phone
• síminn = the phone
• símanum = the phone, in the dative

This is something you usually learn as part of the whole verb pattern:

• slökkva á + dative

It is best to memorize it as a unit.

Yes, very much so.

In Icelandic, slökkva á means switch off / turn off, and the thing being turned off comes after á in the dative.

Examples:

• slökkva á símanum = turn off the phone
• slökkva á tölvunni = turn off the computer
• slökkva á ljósunum = turn off the lights

This pairs with:

• kveikja á = turn on

For example:

• Ég kveiki á símanum.
• Ég slekk á símanum.

So yes, it is best treated as a set phrase.

Sometimes yes, but the meaning is not exactly the same.

• þegar usually means when
• um leið og often means as soon as or the moment that

So:

• Þegar við finnum sætin okkar, slekk ég á símanum. can work, but it sounds a bit more like when we find our seats
• Um leið og við finnum sætin okkar, slekk ég á símanum. emphasizes immediately once we find them

So um leið og is a little more specific and immediate.

Because the sentence describes two related actions with different subjects:

• við finnum sætin okkar = we find our seats
• slekk ég á símanum = I turn off my phone

So the first action is done by we, and the second action is done by I.

This kind of subject shift is very normal:

• Þegar við komum heim, elda ég kvöldmat.
  • When we get home, I cook dinner.

It just means the speaker is part of the group in the first action, but only the speaker does the second action.

Yes — probably these three things:

1. um leið og = as soon as
2. verb-second word order in the main clause:
   • ..., slekk ég ...
3. slökkva á + dative:
   • slökkva á símanum

If you remember those, the sentence becomes much easier to understand and build from yourself.