2002 Mercury Mountaineer

2002 Mercury Mountaineer. I came to a friend house and stop, i turn the car off...I didnt turn the light and radio off. it was just 5 to 6 minute after i came back the car coldnt start so I try jump starting the battery the car still didnt start. when i crang the car it makes a clicking sound the battery seems fine cause i tested it. I dont know whats the problem is. I friend of mine told me maybe it the starter...