From Liquipedia Starcraft Wiki
StarCraft Portal: Mechanics
Mechanics is a player's execution of micro and macro. A player can know how to execute a particular build order but unless the player practiced with it extensively, the execution will oftentimes be sloppy. Fundamentally, mechanics involves pressing the right buttons exactly when they need to be pressed. Playing a StarCraft match involves managing a lot of things at the same time: units, buildings, economy, technology and climb up the technology tree, reacting to the opponent and altering the strategy, etc. The player will generally be cycling through all of these facets are running the way the player intends them to, sometimes known as "going through the motions" or multitasking. One example of a general-purpose short cycle would be:
- 1. Make sure worker units are being produced.
- 2. Make sure combat/attack units are being produced.
- 3. Construct buildings.
- 4. Research upgrades.
- 5. Issue commands to the player's army.
- 6. Scouting the opponent
- Amend unit production or building construction/tech accordingly
- 7. Repeat from #1.
Constantly checking up on the status of all aspects of the game-play will allow the player to execute the actions that need to be executed at the exact moment they are needed. The quicker the player is able to accurately work through these types of cycles, the more refined one's mechanics will be.
Mechanical skill in StarCraft is closely related with a players handspeed (APM), good mechanical players will generally have higher APM.
Guide - Mechanics of Starcraft