Join a counter-terrorist or a terrorist team and try to eliminate the enemy team. Crouch behind an object to protect yourself from the enemy's fire. To shoot, you need to enter scope mode. This mode has a very limited visibility and you will have to stand up, which means your body is exposed and vulnerable to an attack. In certain maps, you can pick up a rocket and use it to deal high damage.
Right click - aim; Left click - shoot;
Space - rocket; A D - right, left;