Soon after pubic hair begins, the penis starts to grow. At first the penis gets longer. After awhile, the penis also gets thicker. The scrotum changes as well. It hangs lower and gets looser.
Testosterone works on many parts of the body.
Toward the beginning of puberty hair grows in the armpits, and you start to develop body odor. This is when it is time to start using deodorant. Testosterone causes the voice box to enlarge, causing your voice to sound deeper. Since it takes awhile, your voice goes through a squeaky period. You may get embarrassed by it, but remember this is something that happens to all guys and it usually doesn't last more than 6 months.