Types of Throws

Different types of throws will give you different experience bonuses and a lower chance of the pokemon breaking free from the pokeball.
A Nice throw will earn you 10 extra experience.
A Great throw will earn you 50 extra experience.
An Excellent throw will earn you 100 extra experience.
A curve ball will earn you 10 extra experience and stack with other throw bonuses. For example, you can throw a curve ball that is also a Great throw.
And all special throws will lower the chance of the pokemon breaking free.

How to Throw a Curve Ball

Wind up the pokeball before throwing it to do a curve ball.
A curve ball will get you 10 extra experience (20 with a lucky egg activated) and a lower chance of the pokemon breaking out of the ball.