Electrum is quite simple once you understand the interface. The 16 buttons at the bottom are 1/16th beats. Choose a patch from the middle - e.g. choose kick, then do a basic four on the floor by pressing buttons 1, 5, 9 and 13.
Then select say snare and press 3 and 11.
Hit the the play button and off it goes.
From the menus you can change BPM etc.
Just for fun, using a Samsung S3 and a USB host cable, I can plug my Korg padKontrol in and play my phone using that!