Ok for all you Zelda fans out there I'm sure this will be an easy qustion......

When you enter Jabu-Jabu, run through this room to the next one and then talk to Princess Ruto. When she walks away and falls down the hole, follow her, then talk to her again; she'll now let you carry her, so pick her up and go through the door behind you. Now get through this room without getting hit; in the next room, head into the lower area and throw Ruto to the other side. Jump on the Switch to make the water rise, swim over to where she is and climb out. Run through the next room without getting hit again; when you get to the door, put Ruto down, shoot the overhead Switch with your Slingshot, pick her back up and head through the door. Dodge the Octorok's attacks until the floating platform gets to you, then go jump on it; when it gets to the top, jump off and go through the door on the right. Now make your way to the other side of this room and go through the door; take the path to the far right and put Ruto on the Switch (stand in front of it and hit the R button). Now head through that door, destroy all of the enemies and you'll get the Boomerang - that should get you going, I'll leave the rest up to you!

In Jabu-Jabus belly I think you have to kill 40 or something like that bubbles in one of the rooms.

Zelda_Fan

If you're wondering where to get it in general, it's in Jabu Jabu's belly, the third dungeon. If you're in Jabu Jabu's belly and wondering exactly where it is, it's in a room with a bunch of bubbles. First you walk into a room with a big tentacle thing blocking the way to most paths, you'll have to go a certain way and open a door by putting Ruto on a switch. You then go into the room, kill all of those bubble things and obtain the boomerang.