How to do a push upWatch
Easiest way is to start off doing kneeling press ups to practice going to the correct depth and position in your push up- keep your head and spine aligned and your nose should practically be grazing the floor at the lowest point, elbows at about a 45 degree angle so not super tight against your body or way out to the sides like you see sometimes (I will say that as you get better at push ups different arm positions can help target different muscles but we'll stick with normal pushups for now). When you do kneeling pressups, there should be an imaginary straight line from the tip of your head to your knees at the bottom of the position. Don't push your weight back into your hips and don't bend at the hips a lot, your knees are just on the floor to alleviate some body weight.
You can practice half push ups, so go from the start of your press up position and very slowly lower your body to the floor, not letting your body collapse but keeping it all slow and controlled. Or the reverse where you start on the floor and push up into that high plank position (imagine it's the second half of your press up here so don't push your hips into the floor to push yourself up but keep your core braced and press with your shoulders and back. It's difficult!)
Incline press ups against a wall or bench make press ups easier, the lower the incline, the harder it is so play around with different levels (maybe on the stairs?) to see what works
Then you can practice full press ups! Don't worry if you can't do it straight away, just keep trying to do one press up with really good form.
When you do your press ups or variations, think about bracing your body right from the very start. From that high plank position, if you press your hands into the ground you'll feel your lats engage down the sides of your back? Keep them engaged, keep your shoulder blades in and down, shoulders and chest wide and open (don't let them sag or hunch), core braced and head and neck in one line. Imagine the movement starting with your strong back muscles, not just bending and stretching your arms.
If you get bored of press up movements, other great ways to strengthen your body for pressups include tricep dips, chest presses using a weight or makeshift (but safe) weight, plank and high plank (arms straight rather than on your elbows), and variations on the plank like doing shoulder taps or commandos (start in high plank, go onto the elbow of one arm then then the other so you're in an elbow plank, then back onto the hand of the first arm then the other so your back in high plank).
Hope this helps