When it comes to playing spin the bottle, the very first thing you'll need is other people unless you want to play by yourself, which would be a pretty sad sight. To begin, find a group of willing friends — the more the merrier! Try to get a group that contains people of both genders so that there are a range of many different combinations of people who can potentially kiss.
Make sure your friends know what they are getting into before you start playing. Kissing is something that's usually reserved for people who really like each other, so forcing people to kiss who don't want to can be really embarrassing for everyone involved. Don't pressure anyone into playing with you who doesn't want to.

Sit in a circle. When everyone is ready and willing to play, arrange yourselves in a circle so that you're all facing inward. Traditionally, this is done on the floor, though there's no reason you can't also do it standing or sitting around a table. Regardless of exactly how you arrange your group in a circle, it's usually best to pick a spot with a tough, hard surface, like a section of hardwood floor. This ensures that the bottle you use can spin well without scuffing or damaging the floor.

Spin the bottle! When you're all ready to play, pick one person to start the game. This person grabs a bottle (or, really, any similarly spin-able object, like a pen, glass, key, etc.) and spins it hard in the middle of the circle of players. After it starts spinning, no one may touch the bottle until it comes to a complete stop.
If you're unsure of how to decide who should spin the bottle first, you may want to try letting the oldest or youngest play go first or having one person think of a random number and starting with the person who guesses closest to it.