Contact the program director of the college radio station you're targeting. After corresponding with her by phone or email, she should be able to determine whether or not the station can use your music. You can generally obtain the program director's contact info by visiting the "Staff" or "Contact" pages on a station's official website.
Send a demo CD of your music to the station you're targeting. Make sure the disc contains what you consider to be your best work. Alternatively, if you are hoping to draw the attention of a specific college radio station employee, email her a link to a website where she can download MP3s of your songs.
Provide the station you're targeting with mini press kits. These kits should include full bios for all the members of your band, a basic facts sheet, your band's discography and a list of your biggest musical inspirations. Additionally, if your band plays a lot of live shows, include a list of upcoming performances.