click the icon that looks like this

then go over your gif and select a part of the gif that you want to add text to (sorry it’s kind of hard to explain)

it should look like this now

then type in the box. once your done, you can move your text around and add stroke, drop shadow, etc. it should look like this:

the font that i use most of the time, well technically all the time is calilbri. only sometimes, which is rarely, i use myriad pro or arial.

but on this gif i used arial (:

hope it helped!