The spells are different for Conjurer and Scholar but your basics will be a low-level heal, a better heal, and an aoe heal. That's a simplified presentation.

For conjurer - cure is your basic spell and medica is your aoe. You shouldn't be using medica unless multiple people are taking damage.
Later you will get cure 2 (bigger single target heal), regen (single target heal over time), medica 2 (aoe heal with regen), and cure 3 (ranged aoe heal).
In general you want to use the lowest spell that will handle things.

For scholar - physick is your basic spell and succor is your aoe .. but it works a bit different than medica. Succor does a basic heal and adds a damage shield. Adloquium is the bigger heal and it also adds a damage shield.