While it would be possible to plug your guitar straight into the input of a surround sound system and use it as an amplifier, you have to be careful that you do not damage your system's speakers when doing this. The tone of your guitar would also be quite bland if you ran it straight into a surround sound system. Luckily, the solution to both of these problems is to first run your guitar's signal through a preamplifier.
Purchase a guitar preamp. Any type of preamp would work to balance the signal coming from your guitar to your surround sound system, but a guitar preamp will give you several tonal options specifically tailored for a guitar. Guitar preamps can be bought at any guitar store.
Run an instrument cable from your guitar to the input of the preamp. Take another instrument cable from the output of the preamp to the input of your surround sound system. You may need to use some type of jack converter to plug an instrument cable into your surround sound system.
Turn on your guitar preamp. Turn the volume most of the way down before you turn on your surround sound system.
Turn on your sound system. You may need to change the settings on you system in order to get the sound to come through all of the speakers.
Play your guitar. Adjust the preamp and surround sound system controls until you find a good volume and guitar tone.