Each band section (percussion, wood-winds, brass, guard, etc.) needs parents to help with different task such as:

Pass on information to other parents in your section

Help decorate during competitions

Provide treats for the sections during some practices

and basically just help the boosters by being a liaison to the rest of your section. 

Those who want to be a section parents will be given a contact list for those in your section.  Through-out the year you will have the chance to get to know all of the kids in your section.  Having additional children in your tribe is a rewarding experience and you will help to make those kids experience in band, a fun and memorable one.