Hit N to get up your Soul tree.
At the bottom your new role will be shown.
Click on it and then hit the Activate button on the right.
You will get a whole blank soul tree with room for three souls.
Click on one of the blank squares that usually have soul emblems and it will let you choose the new soul.
Add points as required.
I have found that it is best to save and close and re-open the soul tree after you have put the points in each soul. Otherwise you get strange things like your selections not showing.
When you have filled the three trees as far as you can/want visit your trainer to get the extra ranks.
Also from your description it sounds as if maybe you have just got the Beastmaster soul. You will find that there is a representative of every soul type wanting to give you the quest to get that type. Unless you have very strong ideas I suggest getting them all before you create your additional roles. You also get the achievement "SOULFUL"