I have not played a Disc priest but twice so I will not teach you guys that, but I have played resto druids up to level 80 so I am pretty familiar, in fact I am still playing my resto druid just played him yesterday, besides from that these steps should help you become a very good healer :D.
1st. What you need to do if you haven't gotten it already is get the Curse client from curse.com make sure it is the Official curse website and get the curse client make an account, or if you want you don't have to get the client or make an account just look up the addon you're looking for.
2nd. The second thing you need to do is look up the addon Healium (My Favorite addon for healing), or Healbot (Second on my favorite list).
3rd. Druids you get your first heal at level 3 Rejuvenation in my opinion one of the BEST heals for druids, at level 12 you get a ressurect spell Revive and another healing spell Nourish you will use Revive to bring fallen people back to life (Out of combat use only), the next healing spell is at level 18 it is Regrowth my opinion 2nd best healing spell after Rejuvenation, next at level 26 Healing touch long 2.5 second cast takes 30% of your mana, I don't ever use it much you guys might though, onto the next healing spell at level 36 Lifebloom 1=1 stack hit 3 times for maximum healing capability each pop is 5.9% of base mana I use this quite a lot actually 3rd in chain of my fav/best heals, next spell is at level 56 Rebirth this is the same as Revive only it can rez a fallen hero in combat neat in my opinion very useful, (Recommended to only use on other heals in raids or tanks), next spell is at level 76 Wild growth quick heals until it reaches max duration then it slows down heals 4th in chain of best heals 22.9% of base mana, next spell is at level 84 Wild mushroom spawns 1 mushroom up to 3 and Wild mushroom bloom will heal nearby allies detonate will damage enemies, those are all the healing spells that are useful for druids you may encounter some I may not have mentioned, this is the way I use my Resto druid healer Druidtime on realm Nathrezim, I have a lot of characters and I will be doing more step-by-step guides on the specs and how to use them effectively, all the information was not researched by me I got all the spells from Thottbot.com or Wowhead.com have fun playing a Resto druid!