The Fx keys make special commands.
F1 : prepare to display help for a command key. Example : if you want to know what happen when hitting the Ctrl key, hit F1 then Ctrl.
F2 : not in use.
F3 : displays the RAM memory left.
F4 : redisplays the document.
F5 : not in use.
F6 : starts the programmation of a key.
F7: not in use.
F8: not in use.
F10 : displays the already programmed keys.
    See the General Help Policy, by a right click on the Help Button (the butterfly) to have a quick view of the PreTeX help.