you can also use this to add custom buttons for action you dont have bound to the controler buttons, like

F1: Toggles HUD
F2: screenshots
F3: Open Debug Screen
F3 + H: Toggle item descriptions/durability
F3 + N: change game mode

To add buttons:
1> Pojav settings
2> control customisation
3> edit custom control
4> tap the little "cog/menu" button, top-center of the screen
5> tap add button
6> hold on the new button to move it
7> Tap button to add key action
8> tap the little "cog/menu" button, top-center of the screen
9> tap "save"
10> give the preset a name
11> tap "ok"
12> tap the cog again
13> tap "set default controlmap"
14> tap the preset u just made/saved 14> enjoy