Evenemanget börjar klockan tio.

Because -et is the definite article attached to the noun.

• evenemang = an event
• evenemanget = the event

In Swedish, the definite article is usually added to the end of the noun instead of being a separate word like the in English.

Since evenemang is a neuter noun (ett evenemang), its singular definite form is evenemanget.

Börjar is the present tense form of the verb börja.

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

Swedish verbs are simpler than English verbs because they do not change for different persons:

• jag börjar = I begin
• du börjar = you begin
• han/hon börjar = he/she begins
• vi börjar = we begin

So börjar is the correct form here because the sentence is saying what happens now or in the future as a scheduled event.

In Swedish, you usually do not need a separate word like at before clock times.

So:

• börjar klockan tio = starts at ten o’clock

The idea of at is built into the time expression.

Compare:

• Mötet börjar klockan tre. = The meeting starts at three.
• Filmen börjar klockan åtta. = The film starts at eight.

Here klockan means at ... o’clock or introduces a clock time.

Literally, klocka means clock, and klockan is the clock, but in time expressions Swedish uses klockan in a special way:

• klockan tio = ten o’clock
• klockan två = two o’clock

So in this sentence, klockan tio means at ten o’clock.

Usually, klockan is the most natural choice when giving an exact clock time.

• Evenemanget börjar klockan tio. = the normal, clear version

In some casual contexts, Swedish speakers may shorten time expressions, but for learners it is safest to use klockan with exact times.

So if you want to say The event starts at ten, klockan tio is the standard form to learn.

This is the normal Swedish main-clause word order:

subject + verb + time expression

• Evenemanget = subject
• börjar = verb
• klockan tio = time expression

So it works very much like English:

• The event
  • starts
    • at ten o’clock

Swedish main clauses usually put the finite verb in the second position, and this sentence follows that pattern naturally.

It can mean both begin and start.

In everyday English, The event starts at ten sounds more natural than The event begins at ten, but both are correct. Swedish börjar can cover both ideas.

So:

• Evenemanget börjar klockan tio. can be understood as
• The event starts at ten o’clock or
• The event begins at ten o’clock

Yes, often you can.

• Evenemanget börjar klockan tio.
• Evenemanget startar klockan tio.

Both can mean The event starts at ten o’clock.

However, börja is often the more general and very common verb for begin/start, while starta can sometimes sound a little more like set in motion / start up, depending on context.

For an event, both are possible, but börjar is extremely natural.

A rough guide for English speakers:

• börjar sounds approximately like BUR-yar, but with a Swedish ö sound that does not exist exactly in English.

A few helpful notes:

• ö is a rounded vowel, somewhat like the vowel in British bird, but with rounded lips.
• j in Swedish is usually like English y
• So börjar is roughly BÖR-yar

You do not need perfect pronunciation immediately, but watch out for the ö and the j.

A rough pronunciation guide is:

eh-veh-neh-MANG-et

The stress is mainly on mang.

A few points:

• the final -et is the definite ending, pronounced clearly
• Swedish vowels are often shorter or more precise than an English speaker expects
• the g in evenemanget is pronounced as a hard g

If you say something close to eh-veh-neh-MANG-et, you will be understood.

Yes, klockan tio normally means exactly ten o’clock.

If you want to be more specific, Swedish can also say things like:

• klockan tio på morgonen = at ten in the morning
• klockan tio på kvällen = at ten in the evening

But if there is enough context, klockan tio by itself is usually enough.

A yes/no question is made by putting the verb first:

• Börjar evenemanget klockan tio? = Does the event start at ten o’clock?

This is a very common Swedish pattern:

• statement: Evenemanget börjar klockan tio.
• question: Börjar evenemanget klockan tio?

Yes.

You can say:

• Klockan tio börjar evenemanget.

This means the same thing, but now the time is being emphasized a bit more.

Notice the word order: when klockan tio comes first, the verb still has to stay in second position:

• Klockan tio
  • börjar
    • evenemanget

This is an important Swedish rule called V2 word order.

If you mean an event rather than the event, you would use:

• Ett evenemang börjar klockan tio.

Compare:

• ett evenemang = an event
• evenemanget = the event

So the original sentence is definite: it refers to a specific event already known in the context.