Є basically means "there is/there are", denoting that something or someone is present, available..
You can drop it in this sentence. Hard to explain without contexts (which DL unfortunately doesn't have):
1) A professor is looking for his student. He walks into a room. Sees a bunch of different people. He asks Тут є студенти? Are there (any) students here?.
2) There are two rooms - one where students are working and one where professors are working. A guy is standing in front of the two doors, points at one and asks his friend Тут студенти? (Are) students here?. The answer goes Ні, тут викладачі. Студенти тут. No, professors are here. Students are here (points at the other door)
Could be other scenarios too.) Hope I did not confuse you more))
Ah, I think I understand! That one-letter word (which I don't have on my keyboard) is used when referring to a mixed group, whereas it is omitted when referring to 2 distinct, separate groups. Is that correct?
I think he is getting at the idea that this is talking about the existence of something with є. I believe it is a bit like the difference in French between "il y a" and "est" (the copula that Ukrainian lacks, if it is like Russian, but which is "je" is Czech).
Тут є студенти? => Are there (any) students here?
Тут студенти? => Are the students here?
A tip to understand this is to compare with Spanish: "Hay estudiantes aquí" - literally, "Have students here". That is exactly what we do in Ukrainian: "є" also means "to have" (e.g. У мене є студент = I have a student), so "Тут є студенти" is, basically, "Here have students" which means "there are" :)
I can add for other languages.
In English (as pointed out above by Skapata):
Are there [any] students here? — Тут є студенти?
Are the students here? — Тут студенти?
Y-a-t-il des étudiants ici? — Тут є студенти?
Sont les étudiants ici? — Тут студенти?
Gibt es Studenten hier? — Тут є студенти?
Sind die Studenten hier? — Тут студенти?
"Sont les étudiants ici?" is not good French. It should be : "Les étudiants sont-ils ici ?"
You are absolutely right. I was hoping to explain the difference, but made an even bigger mess out of it...
Let me throw a Polish example then: Czy są tu (jacyś) studenci? — Тут є студенти?
Czy studenci są tu? — Тут студенти?