Selidba počinje danas.

Selidba is a noun. In this sentence, it is nominative singular, because it is the subject of the verb.

It is also a feminine noun. Its basic dictionary form is selidba.

Serbian does not use articles like a, an, or the.

So selidba can mean either the move or a move, depending on context. English requires an article, but Serbian usually leaves that idea to context.

Počinje is the 3rd person singular present tense form of počinjati, meaning to begin / to start.

It is 3rd person singular because the subject, selidba, is singular. In other words:

• ja počinjem = I begin
• ti počinješ = you begin
• on / ona / ono počinje = he / she / it begins

Here, selidba počinje literally matches the move begins.

Not in the present tense.

In Serbian, present-tense verbs mainly agree in person and number, not gender. So počinje is used because selidba is singular, not because it is feminine.

Gender becomes visible more clearly in some other forms, especially the past tense. For example:

• Selidba je počela. = The move started.

Here počela shows feminine agreement.

Yes, Serbian can often use the present tense for something that is starting today, especially if it is understood as a planned or scheduled event.

So Selidba počinje danas. sounds natural as The move starts today.

You could also say:

• Selidba će početi danas.

That is also correct and is a more explicitly future-style way to say it. The original sentence is simply a very natural present-tense way to express a near or scheduled event.

Danas is an adverb, meaning today.

It does not change for case, gender, or number. It simply gives time information about the action:

• počinje danas = starts today

So it is not a noun in some case here; it is just a time adverb.

Yes. Serbian word order is more flexible than English word order.

The neutral order here is:

• Selidba počinje danas.

But you could also say:

• Danas počinje selidba.
• Počinje selidba danas.

These versions are possible, but they shift the emphasis a little:

• Selidba počinje danas. → neutral
• Danas počinje selidba. → emphasis on today
• Počinje selidba danas. → less neutral, more stylistic or context-driven

English usually has less freedom here.

A learner will usually want to notice two sounds:

• č sounds like ch in church
• nj sounds roughly like ny in canyon

So počinje is approximately:

• PO-chee-nye

And the full sentence is roughly:

• SEH-leed-ba PO-chee-nye DAH-nahs

That is only an approximation for English speakers, but it is a useful starting point.

This is an aspect question.

• počinje comes from počinjati = to be starting / to start (imperfective)
• počne comes from početi = to start / begin (perfective)

In a simple sentence like this, počinje danas is a very natural way to talk about an event beginning today.

Počne is not impossible in Serbian generally, but it belongs to a different aspect pattern and is used in different kinds of contexts. For a learner, the safest choice in a sentence like this is:

• Selidba počinje danas.

Selidba usually refers to a move / relocation, especially things like moving house, moving to a new apartment, or relocating.

It is not the general word for any kind of movement. So in this sentence, it most naturally means a relocation process, not movement in the broad sense.