SetChildIndex / Bring to Front

Hello, I have a movie in which I would simply like to mouseover a movieclip and have it go in front of another movieclip. I understand that the way to do this in as3 is “setchildindex”. Im not much of a programmer and much of my flash is framebased. Can someone help me with the script for this. Ive been trying to make setchildindex work, but its not working.