How do you get all druid forms at level one on World of Warcraft

You get all the forms at different levels.

Bear Form : 10 (Quest from Druid Trainer)
Cat Form : 16
Travel Form : 16
Aquatic Form: 16 (Optional Quest, Trainable otherwise)

Moonkin and Tree of Life forms are talents you get by putting enough points into their respective talent trees. They are sorta in the middle of the trees so you will need to be at least level 40ish to get them.

Flight Form you can get at level 60 from your trainer, it basically give you a free flying mount and the training to go with it. At level 70 you can train the Epic Flight Form if you have the training for it.

NOTE: In the future expansion Cataclysm (currently in Beta), they are switching the levels at which you get cat and bear form. Cat form will be at level 10 and Bear form will be a little higher than that. Also they will be removing the Tree of Life form as a passive form making it a cooldown based ability.