To add dice to the calculation pool, tap the corresponding die in the Available section
To remove dice from the calculation pool, tap the corresponding die in the Selected section
To calculate the probabilities of the dice in the calculation pool, tap the Stats button (which will only appear if there are dice in the pool, and if the pool has changed since the last calculation
To roll the dice in the calculation pool, tap the Roll button (which only appears under the same circumstances as the Stats button)
To switch games, tap the corresponding game icon at the bottom of the screen
To enter fullscreen mode, tap the fullscreen icon (four arrows) in the upper-right corner of the screen next to the title bar
To pin the app to your home screen, ask Google how to do that (I cannot list instructions for every device, operating system, operating system version, browser, and browser version here)
Caveats
I did not design the app to run on a desktop browser. It will run, it just won't look nice (not that it looks particularly nice normally -- it is rather spartan in its appearance)
The app does not support comparing different groups of dice side-by-side
The app does not support calculating attack vs. defence (chance to land a hit) -- that is left as an exercise for the player
About
A dice probability calculator for Star Wars: Imperial Assault to help me make informed decisions in-game