"The people are looking at trees."
Translation:Ti lidé se dívají na stromy.
You can read about reflexive verbs in James Naughton's Czech - An Essential Grammar, section 7.3. You should be able to find it easily and download it for free.
It can, but only when STRONGLY stressing dívají.
The people are LOOKING at trees. or The people ARE looking at trees.
I will add it because Duolingo is not a good place to enforce natural Czech word order. You have to learn it by other means anyway.