You can fill in how many dice you want to roll as well as any modifiers, but for the most part it's already set up with a D20 dice so all you need to do is click the button unless you want it to roll more than one dice or whatever, in which case you fill in the info you need for it.  I did seven D20 dice, or had it roll seven 20 sided dice for me so I didn't have to click it seven times lol.