Press the "Record" button on your loop recorder.
Play a phrase into the loop recorder.
Press the "Stop" button on the loop recorder as soon as you are done playing. On some loop recorders, the "Stop" button is the same as the "Record" button.
Press the "Record" button again to overdub onto your existing loop. In this way you can layer a number of different parts to create a complex loop. Some loop recorders can begin overdub mode automatically after you record the initial loop.
Adjust the speed and pitch as desired. Some loop recorders have one control that affects both speed and pitch, whereas others allow you to alter one without changing the other.