The cycle a game repeats dozens of times a second: read the player's input, update the world, then draw the picture.
Every game, however simple, runs on a loop that never stops. On each pass the game asks: what did the player press? Then it moves the character and the enemies, checks for collisions, updates the score and draws the new scene. This usually repeats sixty times a second, which the eye reads as continuous movement.
Understanding the loop explains why one game feels smooth and another choppy, and why a small number such as jump strength changes the feel of the whole game: that number is applied on every pass. In Fanann 2D Game Design you do not write the loop yourself; you describe the game and it runs, then you tune the numbers with sliders while it plays in front of you. Practical tip: when describing your game, think in loop terms: what the player does, what moves on its own, and when you win or lose. Those three sentences are enough for a playable start.