This menu allows you add a new Event cost, set a default amount that can enabled.
Cost classifications apply to groups of people. For example, you can have a classification for children, adults, members, library card holders, residents, ect.
Simply name the classification and set a default amount. That amount can be changed on the Event Creation form, unless you check "fixed". Fixed sets the price for the classification that cannot be changed.
You can also edit existing cost classifications.
If everything is configured correctly, these classifications should appear on the Event Registration page, when Payment Required is checked.
You can then apply various classifications to the event, allowing you to charge different prices to different groups of people.