Welcome, zahari. hello
EX: People (who are) arriving at Gate 15 will have to go through customs.
EX: ?People (who are) getting there first will get the best bargains.
The first event is happening now; it's actualized, whereas the second event is unactualized. That is, our example sentence is conditional:
EX: People will get the best bargains only if they get there first.
Now actualized; i.e., it's happening at the moment,
EX: People (who are) entering the store right now will get the best bargains.
I would like to ask a question.