Leden börjar i dalen.

Because -en is the definite ending here.

• en led = a trail / a route
• leden = the trail / the route

Swedish often puts the equivalent of the at the end of the noun instead of using a separate word.

So:

• Led börjar i dalen would sound incomplete or unnatural here.
• Leden börjar i dalen = The trail begins in the valley.

The base form is led.

In this sentence:

• led = the dictionary form
• leden = definite singular

A simple pattern is:

• en led = a trail
• leden = the trail

For the same reason: dalen is the definite form.

• en dal = a valley
• dalen = the valley

So i dalen means in the valley.

If you said i en dal, that would mean in a valley.

Because Swedish usually marks definiteness by adding an ending to the noun.

Compare:

• English: the trail
• Swedish: leden

And:

• English: the valley
• Swedish: dalen

This is one of the biggest structural differences from English. Instead of a separate the, Swedish often uses:

• -en
• -et
• -n
• -t

depending on the noun.

börjar is the present tense of börja (to begin / to start).

So:

• börja = to begin
• börjar = begins / is beginning / starts

In this sentence, Leden börjar i dalen, it means The trail begins/starts in the valley.

A useful point for English speakers: Swedish verbs do not change according to the subject.

So you get:

• jag börjar = I begin
• du börjar = you begin
• leden börjar = the trail begins

The verb form stays the same.

This is the normal Swedish main-clause order:

subject + verb + other information

So here:

• Leden = subject
• börjar = verb
• i dalen = adverbial/prepositional phrase

This is very similar to normal English word order:

• The trail begins in the valley.

Yes, you can.

That version means the same basic thing, but it puts more focus on i dalen (in the valley).

A very important grammar point: Swedish main clauses usually follow the V2 rule, meaning the finite verb comes in the second position.

So:

• Leden börjar i dalen.
• I dalen börjar leden.

Both are correct.

But you cannot normally say:

• I dalen leden börjar.

because the verb must come in the second position.

Yes. In this sentence, i means in.

• i dalen = in the valley

That said, prepositions do not always match English perfectly in every sentence, so it is best to learn them in context. But here, in is the straightforward translation.

Not always.

Led can mean things like:

• trail
• path
• route
• track
• sometimes a more marked trail/route in nature or hiking contexts

So the exact English word depends on context. In a countryside or hiking context, trail is often a very natural translation.

A simple approximate pronunciation is:

• Leden ≈ LAY-den
• börjar ≈ BUR-yar (with the Swedish ö, which has no exact English equivalent)
• i ≈ ee
• dalen ≈ DAA-len

A rough whole-sentence version:

LAY-den BUR-yar ee DAA-len

A few notes:

• ö in börjar is a special Swedish vowel.
• The j in börjar sounds like English y.
• The stress is usually on the first syllable of leden, börjar, and dalen.

Yes.

In many sentences, börjar can naturally be translated as either:

• begins
• starts

So:

• Leden börjar i dalen = The trail begins in the valley
• Leden börjar i dalen = The trail starts in the valley

Both are fine in English.

You would normally say:

En led börjar i en dal. = A trail begins in a valley.

Or, if you mean a specific valley but not a specific trail:

En led börjar i dalen. = A trail begins in the valley.

Compare the noun forms:

• en led = a trail
• leden = the trail
• en dal = a valley
• dalen = the valley

Yes, absolutely.

Leden börjar i dalen. is a complete, natural sentence. It has:

• a subject: Leden
• a verb: börjar
• a place expression: i dalen

It sounds like a normal statement you might see in a description of a hiking route or map information.