Extras is anything that you want a user to have the opportunity to purchase while they are registering. This is things like uniforms, water bottles, hats etc. If you don't set up any extras, the user wont see this screen while registering.
1. Go to Registration - Setup
2. Click on the Extras tab...it will show you any items you have for sale, their quantity, price and if you want to keep them available for users to see as they register or not. To add a new item click on the Add button
3. Then fill in the required fields and press Submit
Now your Extra items are set up and available.