Commoner must be your starting 2 levels, and once you level in another class that isn't Commoner, you will no longer be able to take Commoner levels. You never multi-class into Commoner, only out of Commoner.
In 3e/3.5e Dungeons & Dragons, there were several non-player character classes:
The Commoner class allows players various roleplaying opportunities, providing options beyond traditional adventuring. While the class is named Commoner, players can opt to portray different roles, such as a religious devotee, a squire, a promising student of the Art, or simply a common villager.
This class is locked behind Eminence Points. See Eminence Points.
Commoners receive one bonus feat at every level.
Commoners receive an additional 4 CXP for every Commoner level.
The max level of a Commoner is level 5. After reaching level 5, they must choose another class to continue their character's journey.
No Combat XP: Commoners do not receive combat XP. However, they can still earn XP from all other sources. To help mitigate the slow leveling factor, Commoners receive increased hourly XP, starting at double the normal rate, which diminishes as they level up. This ends once they reach level 5, at which point all timed XP is stopped.
Crafting XP: Commoners can receive XP for crafting.
Contribution XP: Commoners receive XP for contributing to build requests, up until level 3.