For keyboard:
Map each button on the keyboard to each player
For Controllers:
Plug in a controller for each player and map them to your [and their] liking [you may need a multi USB for this though depending on how many players are playing]
*Bluetooth controllers connected to the device won't work, they need to be connected via a USB cable to the device's USB port
*There's an option to let the players swap between the keyboard and controller
*If you're using a keyboard, make sure you either remember your keys, or write them down somewhere so you can use it as a reference sheet for what each one does