Boss #1: Aquamentus
Items Required: Sword (would help if you had full health to use beam attack)
Defeating: Simple really. Just use your sword to attack its head. Watch out for the fireballs it spits out, other then that, you're okay. If you had the beam attack, you could stand off in a distance and aim for its head. This is very helpful and an easy way to help defeat.
Boss #2: Dodongo
Items Required: Bombs
Defeating: This boss is truly tricky. You have to lay bombs in its path, and hope it'll swallow them. Try and leave them only when its mouth is open. It takes usually around 3 bombs. Keep trying and you'll get it.
Boss #3: Manhandla
Items Required: Sword and Bombs (optional)
Defeating: The better way to defeat this boss is to drop a bomb near its center, as close as you can possibly drop it. If you want to use your sword or are out of bombs, slash it's claw-like hands to kill.
Boss #4: Digdogger
Items Required: Sword and Whistle
Defeating: You have to use the whistle to break the boss into 3 parts or shrink it into a smaller size. If it breaks into 3 parts, you can defeat one by using your sword and leave the room, then come back. The entire boss will be gone. If the boss shrinks, use the whistle and defeat the smaller Digdogger with your sword.
Boss #5: Gleeok
Items Required: Sword
Defeating: Attack each of Gleeok's heads. Every Gleeok has 2, 3, or 4 heads. Use your sword and hit a head a few times, you should cut a head off. It'll start flying around the room shooting beams at you. Dodge the beams and continue attacking the others heads. Keep doing that until you defeat him.
Boss #6: Gohma
Type: Crab or Spider
Items Required: Bow and Arrow
Defeating: You must shoot arrows at Gohma's eyes. Gohma can be fast, but usually isn't that much of a challenge. Keep a good distance and aim accurately.
Boss #7: Ganon
Type: Gerudo Male, Pig
Items Required: Sword, Bow and Arrow, Silver Arrows
Defeating: At first, he is invisible. You have to slash around the room with your sword until he finally appears. You have to dodge beams he tries to hit you with. If he shoots near you, immediately slash that area, you might hit him. Keep repeating this 4 or 5 times. Ganon should appear brown. Hurry and shoot a Silver Arrow at him to finish him off!!