Of the various surround sound formats introduced over the years, the one that's emerged as most common is called 5.1. With this format, you typically play your audio through five full-frequency speakers, which are fed by five independent channels (left, right, center, left surround, and right surround), plus one dedicated low-frequency subwoofer, which is fed by a channel referred to as an LFE (low-frequency effect). Many manufacturers package systems that include the speakers and amplifiers to play back 5.1 audio. If you're looking to purchase a system, make sure it has six analog inputs, so that it can receive signals from the outputs of your audio interface.
You can place your speakers in a lot of different ways. The following diagram shows an overview of a common layout designed specifically for monitoring 5.1 music playback. The basic idea is that the speakers are placed at an equal distance from where you (the black dot in the center) typically listen. The numbers indicate degrees of separation. Looking directly ahead, the center speaker is considered to be 0° off center. The right front speaker is 30° to the right of the center speaker, and the right rear speaker is 110° to the right of the center. The left front and left rear speakers are mirrored on the left side. The LFE is not indicated in the diagram because subwoofers tend to sound dramatically different depending on where you put them in the room. Exact placement of the subwoofer will be unique for every room, but typically it is placed on the floor in alignment with one of the front three speakers.