How can i tone out my arms?

i am a tiny petite girl. no matter how small i am i still can seem to get thin arms. im 5 foot 3, 111pounds , wear a size kids 16 and im 19 years old. im very tiny but my arms are flabby and thick.what can i do to tone them or make them muscular. i mostly carry the fat in my arm pits and back near my upper arm.