Fijar is to stick or affix one thing to another. It would be used with cola when you want to stick an item to something else, i.e.: use la cola para fijar el papel en la pared.
An interesting usage of the word though is to pay attention. Literally you tell someone to fix themselves on the subject. It is very common to hear “fÃate en esto”, “listen to this” or “pay attention to this.”