Clip art, as its name suggests, is a form of graphic art that makes use of pre-existing images. These drawings / images are either copied or physically cut from existing works in the printed format on a particular topic. The sources of these pictures are either books that have entered the public domain or books specifically published for such use. Logos, mascots, identity and business cards, invitations, letterheads, etc., can be made by cutting or copying the images. Clip art facilitates the availability of a pool of generic art that can be used and reused by non-artists.
Much of the school mascot clipart available also features aggressive looking characters for competitive sports. While this is fine for older kids, you may want to search for something more kid friendly if yours is an elementary school.
When prompted, select "Clip Organizer" for the "Open with..." option and click "OK".