There are many types of baseball pitches. The fastball, the curveball, the slider, the change-up, the forkball, the spitter, the riser, the drop, the sinking fastball, the cutter, etc, etc. Do you need to know all of the pitches? Absolutely not. What you should is how to pitch with a heater first and learn how to locate.
Before you peruse the links below for learning the different pitches, you need to understand a few things. Baseball pitches are the direct result of pitching. Not throwing, but pitching. Pitching is an art form. You must learn to master the art of pitching before trying to learn the different pitches.

It all starts with good fundamentals,i,e, balance, fluid motion, good arm angle, etc. Learning how to throw a simple fastball and throw it for strikes. You can't be consistent until you learn the strike zone and until you have a consistent delivery that allows you to hit your spots.

So my recommendation about baseball pitches? Learn how to pitch using the fastball first. Learn how to change speeds on the fastball, and learn how to locate pitches. This is the foundation for everything else.

You can learn to throw the fastball many different ways. A four seam fastball that rises. A two seam fastball that sinks. A cutter that darts away from a right hander or runs into a left hander. A change up that fools a hitter. Learn how to work the corners, inside, outside. Learn how to work the strike zone up and down. Do you see what I mean?

I don't mean to sound so basic and simple about this, but believe me, these basic things are what keeps people in the big leagues. You don't have to know all of the other pitches. Just learn to pitch using a fastball and variations of it. Than add the rest.