At the age of 13, some girls already look like women, while lots of boys still look like children. Both boys and girls will be very conscious of their bodies and concerned about their appearances. Most boys won't need to shave, but might want to anyway. Girls will probably want to start shaving their legs and underarms.
It's common for teenagers to suffer from acne, which is caused by changing hormone levels. Over-the-counter treatments may help, but if not it's best to see your GP, who may prescribe antibiotics - or the contraceptive pill for girls - as this often controls the problem.