The centre channel speaker is likely the most important investment in your AV speaker package. The centre channel speaker provides the majority of the main audio track and nearly all of the dialogue.
Generally these are placed just below the main TV/projector with audio fired at ear level. These speakers are generally placed on AV stand or cabinet (ideally with isolation feet).
The speakers in this range should generally be paired up with an equivalent left and right channel speaker if used in a Home Cinema setup.