If you have chosen the mage class in Rift you will be surprised at the number of options available to you as far as play style. To give you a quick idea of how the soul trees work in Rift you should know that your class has 9 souls of which you can choose three to be active at any one time. You use the talent points you have been gaining via leveling to gain abilities through the soul various soul trees. By combining these souls in certain ways you can change the play style and roll of your character.
Most commonly the mage is known as a DPS class that is damage per second. This is a basic nuke-em-up type play style meaning all out damage and no utility or buff type spells. There are several soul trees available to the mage class which facilitates this type of play style it is after all the most common.
Rift offers mages a unique opportunity to be healers through different soul trees in the mage class. Many people argue that a mage can suffice as a group healer but only really get picked for raids as healers if their roll will be as a secondary healer or back up healer. Some of the mage souls can really give some great mana conservation and regeneration abilities however.
Another unique roll for the mage in Rift is as a utility class. Utility classes are classes which aid battles by debuffing monsters and buffing up party members. Usually a utility mage will also be able to heal and or do a bit of DPS. Some of the buffs offered through the utility soul trees are really only useful for raiders. Consider your roll in a group and in a raid before choosing a soul tree which is labeled as a utility build.
Many people would agree that Rift has done a great job at opening more group support rolls to DPS only classes. The mage class is just one example of their efforts. Rift allows each character to switch between 4 different saved builds. You should be able to take on each of these builds and test them out as needed. You will always be able to reset your leveling build to pick up more group friendly builds.
If you are seriously considering becoming a mage healer I would suggesting looking at the Chloromancer soul tree. It offers great heal over time options as well as mana conservation abilities. If you are thinking you might want to add a bit of utility to your healer mage try the Dominator soul tree. Mage Dominator's are masters of the damage shield.