For those who are new to Minecraft, monsters (or as most of us call them Hostile Mobs") are mostly found at night time. They cannot spawn if the difficulty is set at peaceful
There are many kinds of these kinds of mobs. You only have to kill only one of them and it doesn't matter what.
Here is a list of the mobs you can kill and what they do best currently in the PS3 edition.
Creeper- Explodes when it is close to you. Very Dangerous to kill.
Zombie- Damages you when it touches you at least. But very easy to kill.
Skeleton- Has the same amount of life as a Zombie, but has a bow and arrows, making it harder to kill. Be swift-full.
Spider- In sunlight, they are neutral. But they will attack you if it is night or you hit them first. You will take damage, but easy to kill with a bow and arrow.
Blaze- Very hard to kill. They shoot fire charges at you and its not fun getting hit by one. Your gonna need at least a sword and/or a bow and arrow. They also drop a Blaze Rod when killed, which is used for portions.
Ghast- They shoot fire charges at you, but it can be pretty easy to kill with a few arrows.
They also drop a Ghast Tear when killed, which is used for portions.
Endermen-Neutral until hit. Like the Slenderman, it can teleport and scare you and will
give you a lot of damage. It is difficult to kill, but will drop an Ender Eye when killed. You'll need it to go to the end.
Cave Spider- Found usually in caves of spiderwebs. They are smaller than a regular spider, but it attacks you and it leaves you off with poison. These things are deadly, so be advised.
Zombie Pigman- They usually spawn in groups, but they are very easy to kill. They also have a golden sword, so it will give you some damage, but not a lot, but BE CAREFULL, if other Pigmen are around, they will attack you as well.
Wolf: They will only attack if you hit them (unless tamed) BUT BE CAREFUL!!, if other wolves are around, they will attack you as well.
Silverfish- (How much I hate these things =-= ) These things hide in normal like stone blocks (any stone block) that are usually found in Strongholds. It can also create a swarm of them if they keep getting killed from surrounding Silverfish blocks. Hard to kill cause they are small, but very weak.
Magma Cubes- They are the Nether Version of Slime, but they deal damage to you and can be split up to tinier cubes. They drop Magma Cream when killed, which is used for portions.
Good luck to all and good hunting <:3 -Frag out.