These are just a variation of the normal pushups which we all know. This variation will also target your core as well as your abs and oblique’s.
To start off get into the normal pushup position. Then lower yourself down as you would for a normal pushup but simultaneously bringing your right knee up and to your side. So ideally once you reach the bottom position of the push up your right knee should be on your side. Then as you push yourself back up you bring your right knee back to the starting position. You then do another one but this time bringing your left knee up. Once you have successfully done both sides you can count that as one rep. The whole exercise is a continuous movement and you keep going until you have finished your specific amount of repetitions. For Push up tips and workouts check this out.