Before you create your first set of classes, you will need to create your first season.
 
This is essentially a folder that will contain your classes that runs over the desired time period that you bill for. For example the term, semester, half term or month.

Make sure the dates here are the time period you are going to be billing your customers for; as this is how Class Manager will create the invoices.

To do this, head to Classes > Create Season, or to Classes > View All and click the 'Create' button at the top right of the page.

Here, it will ask for your season's name and the dates that it runs over:

When you click 'Save' it will open the season so that you are able to create your classes within it.

Find out here how to create a class.