Lie on your side with your arms and your legs extended. Bring your feet slightly in front of you so that you're in a hollow position. You can put one hand down for support if you need (as seen here).
While keeping your navel pulled into your spine, simultaneously lift your arm(s) and legs a few inches toward the ceiling. This is a pulsing movement, so you don't have to lift as high as what's shown here if that's too much for you.
Lower back down, but not completely, so there's a bit of space between your legs and arms and the floor.