Questions & Answers about Okupićemo se u stanu.
It is the 1st person plural future tense of the verb okupiti se.
- okupiti se = to gather / to get together
- okupićemo se = we will gather / we will get together
So the ending tells you the subject is we, even though mi is not written.
This is a normal way to form the future tense in Serbian.
The future auxiliary comes from hteti (to want) in its short form:
- ću
- ćeš
- će
- ćemo
- ćete
- će
With many verbs, this short future form attaches to the infinitive stem:
- okupiti
- ćemo → okupićemo
Notice that the final -i of okupiti drops before ćemo attaches.
A very common alternative is:
- Mi ćemo se okupiti.
That means the same thing.