Final Fantasy XIV Database - Ffxivpro.com

/whm at low lvls
/rdm till the end

low lvls you heal (but cant main heal) you can also debuff and nuke (but depends on your pt format)

mid~lvls, you learn Sublimation thats when it gets interesting! You have a shot at main healing but having someone to help is always nice (note while using sublimation you cant rest since it hurts you...sooooo use it wisely. That changes when you learn Stoneskin tho)

End~lvls you can Aoe Enspells, phalanx, Stoneskin, etc. Main heal like a champ
You can also be invited in manaburns and do some decent dmg (depends on lvl and the camp tho)

this is the most common simple info I can give you
I play around on my friends char that has sch and seen him play the job

:O GL