Gohma

In Ocarina of Time
The mother of all arachnids 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, 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.

In The Wind Waker
Gohma is causing much discomfort to Valoo in Dragon Roost Cavern in The Wind Waker. Gohma is covered in a hard shell. First, use your grappling hook on Valoo's tail that is sticking out of the ceiling and the cieling will cave in, breaking Gohma's shell. After a few times, the shell will be broken leaving him/her vulnerable. Use the grappling hook on Gohma's eye to bring it down to your level and attack with your sword to defeat it. In The Wind Waker, you must defeat Gohma twice, once in Dragon Roost Cavern and once in Ganon's Castle to complete the game.