My biceps, triceps and stomach

So im 14, 15 in aug, and I already go to a gym, but im uder age 4 sum of the machines, like I cant use any of the weight machines, but I can use the rowing machines, tred mills and bikes. Im quite chubby but im trying hard to lose weight and stuff like...

that, I just want to get hard abs and thingd like that how can I do that kinda stuff at home and at the gym? Without over doing it? Lets just say I want to impress the right peeps

well weights really help building the biceps and you can always try the bikes because those actully build your stomach muscles! triceps too I think! hope I helped!