"Snake" is a very difficult labyrinth, but it must be done in order to obtain the Magical Sword.  Though there are many different possibilities to get this job done, the best way to obtain this is to divide "Snake" in three different parts.

Before entering the place, make sure that you got the Blue Candle.  Get the container heart on the northeast corner of the overworld by taking an raft to an island.  That should give you an life gauge of 10 hearts.  Though not required, you will need enough money for Link to shoot arrows.

Now go to the scene near the river where there is an single octoroks.  There is a boat ramp there -- take that boat ramp to cross the lake.  Now you should be where you enter the cave for the Snake Labyrinth.

Now enter the place and take out the Vire and the Kesses.  Now take the key and go left and use the candle to light the room.  Take out as many Vire/Keese as you can and get in the next room.  Take out the Zols and get the key.

Now go up one room and make a right.  Wipe out the Vires and Keeses and continue right.  The next room, avoid the Bubbles while trying to keep the Like-Likes away from you.  Once all enemies but the two Bubbles are wiped out, push the block to the right and go into the passageway for the stepladder.

Once the stepladder has been obtained, leave the labyrinth and grab the container heart on the sea and get more medicine if needed.  If the Like-Likes have ate up your Magic Shield, get a new one.  Now make sure to have plenty bombs upon reentering.

Reenter the labyrinth and do what you did before, only now when you see the two Bubbles and three Vires, go straight up instead of right.  In that room, make a right to a room full of Gels.  Eliminate them and get the map to the labyrinth.  Now, plant a bomb in the north wall.  A secret door should appear.  In that room there are 15 rupies waiting to be found.  Take them and plant a bomb in the east wall in that room.

When you go through that room, take out all the Vires and Keeses and push the block ot the right.  The shutter-door will now open.  Go through that door to take on the Two-headed Gleeok.  Gleeok must be killed with the sword, so if you are going swordless, I would skip this boss for the time being.  Fight this beast on its right side by the sword and when needed, use the medicine.  After you knock off one of his heads, that head will fly around the room.  Don't worry about that head, worry about killing the Gleeok that still remains.

Eventually, Gleeok will be destroyed if that method is done correctly and you will be able to gain the container heart.  Go through the door that just has been opened to claim your 4th triforce fragment.