Custom badges are one-off, manually awarded badges handed out by operators of the Khan application. If you want to add a reusable badge to be earned automatically by any user of the site, you don't want a custom badge -- you'll want to take a look at the
Only site operators can create or award custom badges.
Examples of custom badges:
Note: custom badges may not immediately show up for users after handing 'em out, due to some aggressive caching. If you want users to immediately see their new badges and not wait a few hours, just deploy a new default version.