Good examples of Primary and secondary mechanics

Primary mechanics can be understood as core mechanics that can be directly applied to solving challenges that lead to the desired end state. Primary mechanics are readily available, explained in the early stages of the game, and consistent throughout the game experience. In Grand Theft Auto IV, primary mechanics are shooting, melee fighting, and driving: they are readily available to the player, mapped to the most obvious and tradition-conforming controller inputs and remain consistent throughout the game experience: shooting is always performed using the same button combination, and when players have control, they always have access to that mechanic, provided they have a firearm. Interestingly, this use of the primary mechanics concept explains the design experiment of Orbital: players only have primary mechanics available to interact with the gameworld.

Secondary mechanics, on the other hand, are core mechanics that ease the player's interaction with the game towards reaching the end state. Secondary mechanics are either available occasionally or require their combination with a primary mechanic in order to be functional. The cover mechanic in Grand Theft Auto IV is an example: it cannot be used exclusively to solve the main challenges of the game, but once mastered, it can prove of help to achieve the end state of the game. In comparison, the cover mechanic of Gears of War is primary, since not using it implies the almost immediate death of any game agent.

"http://gamestudies.org/0802/articles/sicart"