The brown is blood.. it is just "dead" blood. It is normal for most women to have this either at the beginning or end of their periods and your period can last anywhere from 3-7 days normally. It is not unusual for a first period to be "light" or shorter in duration.
When your period is light with brown blood like that most of the time that indicates that it's about to go off. During this time there no need for a tampon just wear a pantie liner. Well get comfortable first like knowing how many days it stay on and when it's about to go off .