I'm a bit confused. When does 'se' come before the verb and when after it?
Can I say: these people are looking at trees?
'These' is better translated using 'tito'
Shouldn't it be, "The people are looking at the trees" ?
That is accepted.
Sorry, what is the significance of "se"?
It is a part of the reflexive verb "dívat se", see the Tips and notes, it is important to do so here.
Why not 'The people are looking for trees'?
To look for something means to search for something, to seek something (hledat).