The two-footed jump is a jumping technique, that focusses on the strength of your legs rather than the explosiveness. Both is important, but the strength aspect outweighs the explosiveness.

This is what makes the two-footed jump popular, since it tends to be easier to train your strength than your explosiveness. Sometimes leapers who have the natural ability to jump high, tend to use the single legged jump. 

In case you have the ability to jump off one foot AND off two feet EQUALLY high you should train both techniques.

If you're just starting to train your vertical jump I strongly recommend that you stick to the two-footed jump.

A lot of NBA players use the two footed jump.

But there might be no one better than VC back in the day.

Step One: Getting Your Technique Right

It is really important, that you get your technique down to perfection. I really can't stress that enough.

Think it through:

Imagine you have a Ferrari but really old tyres with no grip. No matter what you try, you will not be able to convert all your engine power to speed. A lot of power is lost because of the low amount of grip.

It's the same with your vertical jump if your technique isn't good you will not be able to jump as high as you actually could. That way you will not see your improvements in the strength and explosiveness department. And this makes you lose your motivation sooner or later.

Check This out:

Just watch closely how Nate takes off

Exercises To Train For The Two-Footed Jump