Why do you have a hole in your butt?

The hole in your butt, called the anus, is there, primarily, for excretory purposes. At the end of the large intestine lies the rectum. By the time food gets to the rectum, it has already been digested and turned into fecal matter (poop). The anus is there so you can get rid of the fecal matter via defecation (pooping). A few organisms only have mouth holes, so everything goes in and comes out the same hole. Thankfully, humans have a hole designated to each task, so we don't have to defecate from our mouths.