Hi mate, welcome to the forums and to the Shaman class!=)
Well, the three talent trees are Enhancement, Elemental and Restoration.
Enchancement is the melee-based tree. It focuses on improving your melee damage and making the totems that improve your melee capacity better. This is the best leveling tree most of the time, I think most people would tell you that.
Elemental is the casting-based tree. It focuses on improving your spell casting times and your spell damage. This is also a so-so PvE tree, although in the earlier levels you might have more downtime while leveling than you would with a Enhancement build.
Restoration is the healing-based tree. It focuses on improving your healing spells casting times and their effects. This is not a very good soloing or leveling tree, unless you spend most of your time grouping and healing your teammates. This is the most instance-based tree and it will make you loved in groups.
So, a summary of this:
Enhancement for fastest soloing and leveling ability, and more melee based fighting.
Elemental for high damage spellcasts and faster casting times than other builds.
Restoration for a Shaman who groups a lot and intends to heal his teammates while doing so.
Hope that's a good answer to your question. Good luck!