"Look at the airplanes."
Translation:Seall air na plèanaichean.
so when we say "look at" in Gaelic we are saying "look on"?
Yes, the usage of preposition rarely translates directly between languages. It’s common that you need to learn what preposition to use on a per-phrase basis when learning a new language. ;-)
(Also, according to Colin B.D. Mark’s dictionary, seall might also be used with ri with besides air on, eg. sheall e ris a’ chleoc he looked at the clock)