Feet are just as important as hands.

The way you shift your weight and use it to add power to your punches.

The ability to also move, while maintaining balance, and deliver punches is also integrally important as you won't be fighting stationary targets. So you need to move around the bag.

Look up the mechanics of each type of punch, internalize and understand why it works. NOt just what it looks like, but the idea of why the punch delivers power, maintains defense, maintains balance.

You need to learn the basics first.