On this page of our Minecraft guide, you will find information on how to tame a dog or a cat. This way you will get your first companion.
Taming a dog
Dogs are, to all intents and purposes, tamed wolves, which get a collar and change looks. A dog responds to sit/up/ attack commands and is very effective against mobs. To tame one, you need meat and/or bones. Approach the wolf and feed it by holding the object in your hand and pressing the action button. After several attempts, you can call it yours.
Taming a cat
Taming an ocelot (to make it a cat) is similar but, you need to serve the ocelot with raw fish. Cats are definitely more difficult to tame, but it can help by keeping Creepers away. It is best to catch the ocelot with lead, to make it unable to escape. You need to carry a lot of fish with you, because the animal is, usually, not easily tamed. Between the successive bits of fish that you serve, you need to take some time. After it is tamed, the cat will change its color to black, black and white or ginger.