Evicting ex girlfriend from my house

Hello, me and the mother of my child are no longer together and she refuses to move out of my house. She is not on the mortgage, and her name is not on any of the bills to the house. Can someone please help me out with the process to get her out of my house and explain it to me like Im stupid. I want to make sure Im doing it correctly, please any help would be appreciated.

Location: St. Louis County, Missouri