Gohma is the boss of Dragon Roost Temple and overall is a very easy boss to kill once you know how to damage him, which can actually be a little hard to figure out at first. Here is a guide on how to kill the Dragon Roost Temple boss.
When you enter the room you will be faced with a large pool of lava. The boss will come out of this pool and start attacking. There is very little you can do to dodge the attacks and you will find yourself dead pretty quickly. The trick here is to look up! You will see the dragons tail hanging out of the roof.
Use your grappling hook to grab onto the dragons tail and swing over to the other side of the room. This will cause the roof to fall down on top of the boss and hurt it. Do this 3 times and you will break the shell off the boss.
Once the hard shell has been broken off the boss, he will be vulnerable against your sword attacks. His eye in particular is his weak point. Jump down to ground level and wait for the boss to come down low to attack you. When he does, attack his eye with everything you got. It should take a few strong attacks to take him down and that will be the end of the boss.
If you need any additional help, here is a video guide on how to kill the boss.