Every user's collection begins in a Content Category. Examples of a Content Category include CS:GO, Streamers, and other verticals within the app. Within the Content Category, users have different Seasons or designations for content released over an extended period of time.
Seasons can be found as a title bar when you enter the Card Library (three overlapping card icon)
Each Season will have different Sets and Collection Tiers. Some sets include Core Season Cards (lasting throughout the entire season) and Special & Limited Edition (timed releases) Different Content Categories will have different types of Sets. CS:GO has Events and Streamers have clip oriented collections including Clip It! and Clip of the Day.