Can you be a little more specific? "Customization" can involve anything from minor appearance tweaks to some pretty involved feature addition/modification. At the extreme end, it can involve writing a fairly extensive content management system for a complex website that just happens to feature some forum-style areas. The "themers" who know how to change colours, fonts and graphics might not be any more able than yourself if your needs are anything beyond the basics.
Oh, and "Google it" isn't a very helpful response.