From console in Counter Strike Global Offensive, you can change game options and parameters such as FPS, quick volume control, aim and other settings. But before using it - you need to enable console in game settings.
Turning on the console:
Launch the game, go to Settings > Game Settings > Enable Developer Console (~)
By default settings, to open a console you need to press "~" button (located between the TAB and ESC buttons), but this button can be changed in the "Keyboard and Mouse"> "Open and close console" settings.
You can check All CS:GO Console Commands here