Archetypes are specific to the many worlds of OSR+ and only apply if the GM chooses to include them in his campaign. An archetype is similar to a kit or class, in that it imparts a special ability you can use in the game. For example, in A Quest of Queens, The Executioner archetype lets you do the following:
You will find archetypes on the OSR+ when you visit a particular world of OSR+.
Archetypes in the Character Creator
You can access archetypes in the Character Creator if you have activated an edition that includes them via your Realm Settings.