I just push it down flat, hold it down and try to keep from overfilling the center so that it doesn't overflow and get on my fingers- but after using a glue gun so much, my fingers are almost immune to glue gun heat.
Once I fill the center, and tap the top/center down- it can get hot, tho... Sometimes I sit a bottle of glue on top to hold it down flat til it dries- I have put on one of those rubber finger covers- to use if you're shuffling thru lots of papers- what are they called? Grips? That can help you not feel the heat of the glue.
Hee hee....I call them "Thumb Condoms"....