The blood colors everything red and brown. The bleeding is not painful in itself, but cramps that sometimes come with your period can be painful. A girl's first several periods are often what are called anovular - this means you are menstruating but not ovulating, there is no egg being produced. These periods tend to be light, irregular and often painless. Sometimes they are not, though.
Periods are very individual.
You might get cramps your first time. It definitely has an odor. Menstrual fluid starts to smell when it is in contact with air. So a pad you have been wearing all day at school can get pretty strong smelling. Also, you might find that the fluid that comes at the end of your period has a stronger smell than the more liquid flow at the beginning.