Collimation is the proper alignment of the optical elements--lenses and mirrors--in your telescope. Collimation is important for getting the best out of your scope. Poor collimation will result in optical aberrations and distorted images.
With your NexStar SLT refractor (lens-type) scope, there is no user-adjustable way to collimate the optics. If the scope is poorly collimated, it needs to be returned to Celestron for warranty or non-warranty service.