By default, koala records to a pad only whilst your finger is held down. If you want it to keep recording (e.g. because you want to use both hands to make a sound like on a guitar or making a hand clap), there are 2 options.
1. When pressing the pad, swipe up to lock it into recording mode, it will carry on recording til you tap it again.
OR
2. go to the General settings of koala and turn off “Hold to record” – this will make each pad start recording on the first tap, and stop on the second tap.