How can i make my start menu stay at the bottom of my screen?

Hi!It's Angela again.I would really appreciate any help if someone can tell me how to stop my start menu from moving around on it's own.It's always changing position.It is so aggravating.Sometimes it's on top,sometimes it goes to the left side of the screen,sometimes it's on the right side.Please tell me how to make it stay on the bottom of my screen.Thanks sincerely to anyone who can help