If you don't know what you're doing, using console commands can cause your game to malfunction !!!
Executing the wrong command can cause your game to stop working normally - furthermore, you may not become aware of such malfunctions right away, and you may not be able to trace their cause.
They can cause problems like making quests impossible to complete, altering your game's display, all kinds of game behaviors, your ability to play your character, and your ability to play the game at all.
Solutions are not always easy, and may involve losing saved games or reinstalling your game.
Create a permanent saved game before using the console. (This mitigates only some kinds of risks.) If you need to use the console to fix a glitch, try to use the least powerful command possible.