How can i build muscle mass?

i think they don't lay around and watch tv all day...ya its summer its easy to be lazy and every now and then its alright but just go do stuff. Ask friends to go play football or basketball or something and get a game going that way your being active. If you go to a gym do weights with lots of reps with low weight and that way you tone your body and you will look cut pretty quickly depending on how much over weight you might or might not be.