What is an enema and colonic?

I've done a little search on this. But I'm still not understanding the process of this, and the tools. I do know it has something to do with cleaning the colon. But why does one have to do both the shakes and an enema/colonic if they are bowels cleanser? Are enemas/colonics not effective enough to be used as bowels cleansers themselves? I'm confused as to what an enema/colonic is, can someone please explain? Thanks. Tweet