To get to the Forest Temple:

     The first order of business - Find the Forest Temple. It is located in the Lost Woods. Go through the Lost Woods using this path : R L R L C L R. About halfway through, an elf will block your path, and say only Saria's friends can pass. To prove you are one of her friends, get the Ocarina out and play Saria's Song.
     You will now have to get past 5 huge guards of the Forest Temple. You can sneak around them or kill them with bombs. When you get to the steps that lead to the temple, dodge the huge monster's attacks and go around him, you don't have to kill him. Once you are at the Temple, talk to Sheik and learn the Minuet of the Forest.
     When you are done talking to her, get out your hookshot that you got at the graveyard. Point it at the tree limb directly above the ledge. Enter the Forest Temple.

To beat the Forest Temple:

     You enter the temple in a small field. To the right are some vines, climb them and kill the gold Skulltula at the top. Get on the top of the tree, and jump to the other limb. On the top of that tree, you will find a chest with a key inside of it. Now get back down to the ground.
     Kill the wolves and enter the building. You enter a room with a spider. Wait until it turns around, then kill it. The next room will show a cut-scene of the ghosts stealing the light from the torches.
     When that is over, go to the big block to the left. It won't move, and it has the same engraving of the Temple of Time. Stand next to it and play the Song of Time on the Ocarina. When it disappears, go through it. In this room, go to the right and up the vines. You might want to kill the Skulltulas with your hookshot first.
     When you get to the cave entry, go in it. Defeat the 2 floating skulls to get the map. Then go on and defeat the plant on the balcony. Aim your hookshot at the target above the other balcony, and shoot it. After you step on the switch and drain the well, jump off the balcony and go into the well you just drained.
    Inside the well, grab the 2 hearts and the small key and climb up the vines. After that, leave this area through the door.
    In the main room, go through the door that is just opposite of the entrance door. Now you will fight a floating skull. Just stun it with the hookshot and hit it with your sword. After you kill it, go to the next room. You will fight the Knights for the first time. After you defeat them, you will get another small key.
     Go back to the main room and to the right. Unlock the locked door with a key. Kill the Skulltula with the hookshot. Go to the next room. Go straight, up the ladder, to the right, up the ladder and to the left. When you get to the arrows, pull the big block out of its hole, and push it on the arrows. When you get it to the end of the hall, go back to where the block used to be, and follow that path to the right. Now you can push the block forward ontop of the other block.
     Now jump ontop of the block, and jump onto the platform. Then follow the cave until you get to the next block. Pull it as far as it will go. Now go back down to where the first block's starting point was. Climb up the ladder and head to the right until you find the pink block. Now push it as far as it will go. Now head back to where it is on the other side. Now push it down the hall as far as it will go. Climb up the blocks and into the next room. Kill the floating skulls and unlock the door.
     This might be one of the weirdest parts of Zelda 64. Walk through the twisted corridor, and into the next room. Jump to the door and unlock it. Go down the hall past the black picture and go down the stairs. Open the door. Fight the skeletons. Get the bow and go back to the room before the twisted corridor.
     Look above the entrance to the corridor and shoot the eye with an arrow. This should straighten out the twisted room. Walk through the twisted corridor to the next room. Get the key out of the chest and jump down the hole. Fight the skulls to open the door. Exit this room and turn right until you get to a door on the right. Go through the door and kill the hands, to get the next silver key.
    Exit this room and go through the one on the right. You must go to the room before the corridor again, so turn right and follow the path until you get to the eye. Shoot the eye so the corridor is twisted again.
     Now walk through until you get to a picture with a ghost in it. Shoot the picture. The ghost will now go to another picture. After you shoot all the pictures on the wall, the ghost will come to life. Z-locking and firing arrows at it while it is visible is the best way to kill it. Get the key out of the chest that appears, and walk through the next room.
     Go past the opened chest and to the next room. Shoot all of the pictures with ghosts on them to fight the next ghost. Kill her to get the Dungeon Compass. Now walk up the stairs and through the door to another upside down room. Go through the path on the right to get to a locked door. Open it (you should have a key).
     This is the cool, but hard part. Stand on one of the moving platforms. Face to the right and you should see a frozen switch. Get your Bow out. Face the switch on one of the moving platforms. When the fire on the torch is lined up with the switch, fire your arrow. It should melt the switch. This will twist the corridor.
     Go back to the twisted corridor. Walk to the end and jump through the hole on the floor. You should now be in a room with checkerboard floor. You must plan your path carefully, as the ceiling is falling and rising. Step on the switch on the right side of the room halfway to the other side. Also, if you want arrows, get the treasure chest.
     When you leave, you will encounter another room with a ghost picture on the wall. Shoot it with your bow. The blocks will fall from the ceiling. You must arrange them so they look like the picture on the wall (that you just shot).
     After doing that, kill the ghost that appears using the same strategy you used for all the other ghosts. Get the arrows she drops after you kill her, and go through the unlocked door. Kill the spider and go to the next room. On the balcony, there is nothing to do but jump, so jump.
     Go to the center of the room. When the ghost splits apart, hit the real one. You can tell which one is real, because the real one spins around 1 more time than the other ones. After hitting the real one about 5-6 times with arrows, go to the elevator that pops up.
     When you get to the bottom of the elevator, get off of it. Stand on on side of the big blocks sticking out of the wall. Pushing it long enough will turn the whole room. You should push it until you can reach the first switch. After you step on that, move the wall around until you get to the second switch. Step on it and move the wall until you find the third switch.
     This switch should open the main gate to the boss. You need the big key to open this door. Go through it, and take a right until you get up the stairs. Walk on to the Triforce ground. You will now fight Phantom Ganon (weird, eh?).
     When fighting him, hit him with arrows 3 times. There are 2 of him, but only one flies out of the paintings. After you knock him off his horse, you must deflect the energy he shoots at you. You deflect the energy he shoots by hittin the lightning he throws at you with your sword. After he falls and dies, the REAL Ganon will talk to you. Get the heart container then walk into the light.

     After you talk to Saria, and get the medallion, you will be back at the Deku Tree. The Deku sprout will talk to you and tell you the truth about many things. He will tell you that you must now save Hyrule!

     Now, if you have not already, you must get Epona, the horse.