You gain more shapeshifts as you lvl
the first one, which is bear form, you gain when you ding lvl 10.
you get it from a quest you'll get from your trainer.
IIRC, at lvl 16, you'll get a quest to learn how to shapeshift into aquatic form.
at lvl 20, you'll learn how to shift into cat form (this is taught from the trainer)
at lvl 40 you get your final form, which is dire bear. this is just a upgraded version of "Normal" bear form.
Optionally, you can get forms from talent points. these are moonkin aka boomkin from the balance talent tree, and tree of life from the restoration tree
