Lie on your back knees bent, find your hip bones and move inwards around 2 inches, cough and you will feel a muscle under your thumbs contract. This is the muscle you want to learn to switch on.
Play around with squeezing your tummy and drawing your belly button into your spine to work out what cue works best for you to switch this muscle on.
Keeping your hands on your tummy, switch this muscle on and breathe. When your breathe out float your leg up and extend it out as shown, breathe in and when you breathe out put the leg back down to the starting position.
Repeat with the other leg. This completes one repetition.
If you feel the muscle switching off, take a break and reset. With practice you will quickly be able to keep it switched on for longer.