MDA

So one of the first things we got to learn at my school is MDA ( mechanics, dynamics and aesthetics).
This is how you basically design a game. We got to train our MDA skills with a game called space invaders which we had an assignment to explain what the MDA is in the game.
What the player see first when they play a game is usually the aesthetics, if they play it longer they might notice the dynamics but our job as game designers are to first get a clear vision on what we want the player to feel when they play our game and after that work on the mechanics.

The mechanics is the rules of the game, what can be done by the player? How the game is build up.

Dynamics is the chain reactions inside the game, if you click on button A what happens next? The input and the output. And also how the players interact with the game.

Aesthetics are the feeling of the game, how the players feel when they are playing the game? The emotional response.