Documentation of classes in the Roblox API is done in the Class namespace. The list of classes can be found at Category:Classes or Class reference.
Templates[]
Articles about classes use the {{Infobox class}} template to add an infobox and categorize the page. Members are documented automatically using {{member list}}. The {{class link}} template is used to link to class pages.
Most of the information used by the infobox and {{member list}} comes from the API dump using Module:APIDump, but information about class icons is maintained at Module:Class icon.
The version numbers used in parameters can be found using the Roblox API Reference maintained by Anaminus.
Removed classes[]
Classes that have been removed from the API are still documented. The infobox template will add them to Category:Removed classes when the removed in parameter is specified.
Information about removed classes must be added manually to Module:RemovedAPI, as they are no longer part of the API dump. That module uses the same format as the JSON API dump converted to a Lua table.