HOW DO YOU USE YR WECAM WHILE ON CHAT W/WINDOW 7?THANK YOU,CAMILLA?

I HAVE WIDOW LIVE MESSENGER,DOWNLOADED THAT ,STILL CAN,T DO IT!IMY FRIEND SAY,S FIRST GO TO FILE,I DON,T HAVE IT ON TOP,LEARN HOW TO USE WEBCAM WHILE CHATTING,THANK YOU,SINCERELLY,CAMILLA