To se desilo juče.

To is a neuter singular demonstrative pronoun. In this sentence, it is the subject, so it is in the nominative.

A useful thing to notice is that the verb form agrees with it:

• to → neuter singular
• desilo → neuter singular past form

So the sentence is built to match grammatically.

Se is part of the verb desiti se, which means to happen.

So you should learn desiti se as a whole expression, not as desiti plus a separately translatable se.

In other words:

• desiti se = to happen

In this sentence, se does not mean itself in the way an English learner might first assume. It is simply part of the Serbian verb.

Desilo is the past participle form, and it agrees in gender and number with the subject.

Because the subject is to, which is neuter singular, the verb also appears in the neuter singular form:

• masculine: desio se
• feminine: desila se
• neuter: desilo se

For example:

• Problem se desio juče. → masculine
• Greška se desila juče. → feminine
• To se desilo juče. → neuter

That is a very common question.

In Serbian, past tense is often formed with an auxiliary, but with reflexive / se-verbs in the 3rd person singular, je is normally omitted.

So you say:

• To se desilo.
• Šta se desilo?
• On se vratio.
• Ona se nasmejala.

Not:

• To se je desilo
• Šta se je desilo

So To se desilo juče is the normal modern form.

By contrast, in other persons or numbers, the auxiliary appears:

• Ja sam se vratio.
• Oni su se vratili.

Yes. Desiti se is perfective.

That means it refers to a single completed event. Since juče points to a specific finished time in the past, the perfective verb fits naturally.

So:

• To se desilo juče. = one completed event happened yesterday

If you wanted to talk about something that used to happen or was happening repeatedly, you would usually use the imperfective partner dešavati se:

• To se dešavalo često. = That used to happen often.
• To se dešavalo ranije. = That was happening earlier / used to happen earlier.

Yes. Serbian word order is fairly flexible.

The sentence To se desilo juče is a normal, neutral way to say it, but other orders are possible depending on emphasis:

• To se desilo juče. → neutral
• Juče se to desilo. → stronger emphasis on yesterday
• To se juče desilo. → also possible, with slightly different information focus

One important rule is that se is a clitic, so it usually appears very early in the sentence, often in the second position.

Because juče is an adverb, not a noun or adjective.

Adverbs do not decline for case, gender, or number, so juče stays the same.

It simply tells you when something happened:

• juče = yesterday

Compare this with nouns, which do change form depending on case.

They are very close in meaning, and in many contexts they are interchangeable.

So these both work:

• To se desilo juče.
• To se dogodilo juče.

For many speakers, desiti se sounds very common and everyday, while dogoditi se can sound a little more neutral or slightly more formal, but the difference is not huge. Usage can also vary by region and personal habit.

No, not with the meaning to happen.

For this meaning, you should learn the verb as:

• desiti se

So a learner should treat se as part of the dictionary form in this case.

Sometimes yes, if the context already makes it clear what you are talking about.

For example, in conversation someone might simply say:

• Desilo se juče.

But to is useful when you want to point back to a specific previously mentioned event, situation, or fact.

So:

• Desilo se juče. → happened yesterday
• To se desilo juče. → that happened yesterday

The version with to is more explicit.