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. You may be able to smell your menstrual fluid, but don't worry, other people will not. Probably not, even though there are menstruating women everywhere you go. Wash with mild soap and water every day of your period if you are worried about it.