An activity (Activity Category) simply put are a grouping mechanism for the type of events you offer. For Education Organisations this is usually the title of a course, for example Exercise to Music (ETM) or Personal Training (PT). It is not possible to create a module without an Activity.
To add an Activity navigate to MODULES > ACTIVITIES and select the "+" button. A form will load as shown below.
Users only really need to enter a TITLE and then select if they want to use the default Schedule Colour scheme or if they want to customise colours so that it is clearly visible on the Schedule.
We recommend that Education Organisations colour Activity Categories so they can quickly see events on the Schedule. In the screen shot below you can see specific workshops, events and exams all in different colours - making it easy for Users to scan the Schedule and find the bookings they are looking for.