When creating a custom character you are able to choose your character's base power. There are many base power's to choose from and each power will tell you what role your character will be best suited for.
There are a number of healing powers to choose from, however, it appears that Nature and Sorcery are currently the only healing powers that come with the free version of the game (if I am mistaken let me know and I can adjust this solution accordingly).
Upon reaching level 10 this achievement should unlock but there is a chance that the achievement will not unlock on time. If you hit level 10 and are not awarded with an achievement you will need to simply back out to the character select screen and then log back into the game, at this time the achievement should unlock instantly.