Here's a step-by-step guide on how to learn to do push-ups:

1. Lie down on your stomach and place your hands slightly wider than your shoulders.
2. Extend your legs back and balance on your hands and toes.
3. Keep your body and back straight.
4. Pull your belly button toward your spine to tighten your core.
5. Lower your body until your chest nearly touches the floor or your elbows are at a 90-degree angle.
6. Push back up through your hands and fingers until your arms are fully extended.
7. Repeat this exercise in sets and reps according to your fitness level.

If you're a beginner, you can start with easier versions of push-ups while more advanced exercisers can use challenging variations. You can also break the movement down into small, doable exercises.