Gohma
The mother of all spiders inside the Great Deku Tree, Gohma is your first boss in OoT. As soon as you enter the room, whip out your slingshot and Z-Target her eye. When it turns red, shoot it and she will be stunned for a few moments. This gives you the opportunity to hack away with your Kokiri sword. If you don't defeat her the first time(which you probably won't), Z-target her again as soon as she get up, and wait until she's up on the ceiling. She will try to unleash her babies on you; when her eye turns red, unload with your slingshot. However if the babies still come, Z-target them and defeat them quickly (be careful when their eye turns red, they will attack). When Gohma comes back down, continue with the same pattern as before to defeat her and earn your prize: a Heart Container and the Kokiri Emerald.