Once the quest begin, go into the cave before you.  There you are equipped with the Wooden Sword.

Then leave the cave and go north to take out the Octoroks.  Don't panic when you first see these creatures.  They're weak compared to later.  Kill them and get the rubies and small hearts.  Then go east to find more Octoroks, but watch out for leevers coming out from the ground.  Keep going north until the scene where there is a long bridge, and avoid Zola's fireballs as Link's tiny shield cannot block them.

Go across the bridge over the lake.  Now enter the cave above and begin your hunt for the Triforce!!