Well, the hooded enemies are wizzrobes, best taken out with your sword and some patience and dodging. Also, the magic shield deflects their magic. One hit of the magic sword should kill the red ones, which are the ones that appear suddenly (in line with you), fire off magic, and quickly vanish.
Ganon uses a somewhat similar style of attack (stealth and projectiles) He stays invisible and fires off boss fireballs at you from various points in the room. I've been told he moves in a circular path and reverses direction when hit. Anyways, you can beat him with a sword and finish him off with the silver arrow.
The red ring is in the top right corner on the first quest. The room is not marked on the map, similar to the eyes. (I played Zelda for at least a year before I knew about this.)
PS: Just remembered where the silver arrows are as well. It's in the topmost room on the leftmost side under a hidden staircase. You have to take a passageway in addition to the initial passageway to get to the room below it, but I forget from where.