Deltagaren anmäler sig till evenemanget.

Deltagaren is the definite singular form of deltagare.

• en deltagare = a participant
• deltagaren = the participant

Swedish usually puts the definite article at the end of the noun instead of using a separate word like English the. Since deltagare is an en-word, its definite form is deltagaren.

Because in Swedish, the definite article is often attached to the noun as a suffix.

So instead of saying something like the participant, Swedish says:

• deltagaren

The same thing happens with evenemanget:

• ett evenemang = an event
• evenemanget = the event

A separate word for the is only added in some other structures, especially when there is an adjective, for example:

• den nya deltagaren = the new participant

Anmäler is the present tense form of the verb anmäla sig.

• att anmäla sig = to register / to sign up
• anmäler sig = registers / is registering

A very common pattern in Swedish is:

• infinitive ending in -a
• present tense ending in -r

So:

• anmäla → anmäler

Other useful forms:

• anmälde sig = registered
• har anmält sig = has registered

Sig is a reflexive pronoun. It is used because the expression is anmäla sig, not just anmäla, when you mean register oneself / sign oneself up.

So the idea is literally something like:

• The participant registers themself for the event

In natural English we usually just say registers for the event, but Swedish keeps the reflexive pronoun.

It is not optional here if you want this meaning.

Because sig is the normal third-person reflexive pronoun in Swedish.

It is used when the object refers back to the subject:

• Jag anmäler mig = I register
• Du anmäler dig = you register
• Han anmäler sig = he registers
• Hon anmäler sig = she registers
• Deltagaren anmäler sig = the participant registers

So sig does not mean specifically himself or herself only; it works as the reflexive form for third person in general.

Yes. This is an important point.

• anmäla sig = register, sign up
• anmäla något / någon = report, notify, announce, register something/someone

For example:

• anmäla sig till kursen = register for the course
• anmäla en stöld = report a theft
• anmäla någon till polisen = report someone to the police

So if you remove sig, the meaning often changes quite a lot.

Because the verb expression anmäla sig normally takes the preposition till when you say what someone is registering for.

Examples:

• anmäla sig till en kurs
• anmäla sig till ett lopp
• anmäla sig till evenemanget

This is a good example of why prepositions should usually be learned together with the verb. English for does not always match Swedish för.

Because evenemang is an ett-word.

So:

• ett evenemang = an event
• evenemanget = the event

Swedish definite endings depend on the gender of the noun:

• en-word → usually -en
• ett-word → usually -et

That is why you have:

• deltagaren
• evenemanget

The basic word order here is:

subject + verb + reflexive pronoun + prepositional phrase

So:

• Deltagaren = subject
• anmäler = verb
• sig = reflexive pronoun
• till evenemanget = prepositional phrase

This is normal Swedish main-clause word order.

If you move another element to the front, Swedish still keeps the finite verb in the second position:

• I dag anmäler deltagaren sig till evenemanget.

That verb-second pattern is a major feature of Swedish.

For a yes/no question, Swedish usually puts the finite verb first:

• Anmäler deltagaren sig till evenemanget?

With a question word, the question word comes first, and the finite verb still comes before the subject:

• När anmäler deltagaren sig till evenemanget?
• Varför anmäler deltagaren sig till evenemanget?

So the statement:

• Deltagaren anmäler sig till evenemanget.

becomes:

• Anmäler deltagaren sig till evenemanget?

You can change the tense like this:

• Deltagaren anmälde sig till evenemanget. = The participant registered for the event.
• Deltagaren har anmält sig till evenemanget. = The participant has registered for the event.
• Deltagaren ska anmäla sig till evenemanget. = The participant will/is going to register for the event.

Also, Swedish often uses the present tense for future meaning when the context is clear, just like English sometimes does:

• Deltagaren anmäler sig i morgon. = The participant is registering / will register tomorrow.