How to get tone and skinnier arms?

I started lifting weights just 5 pounders with about 20 reps, and I'm pretty strong I guess. I can do pull ups, or chin ups watever their called. But my arms seemed to get bigger. :( It maybe muscle but when I flex it my arm gets wider and I have a small small muscle bump, but it's just not like other ppls. I cant really explain it. Anyway I want my arms to look toned and defined, not flabby. Plz help.