Girls can use a sanitary napkin, or a tampon, to collect the flow of menstruation blood.
It’s made of absorbent material and stuck to the crotch of panties with an adhesive strip.
Sanitary napkins (also called pads) come in many sizes. Try different ones and see which you like best.
Most girls have to replace the sanitary napkin after about 4 hours to prevent it from leaking through. If you loose a lot of blood you have to replace it more often.

See also: menarche, menstruation, menstrual cycle.