How do you use grenades in half life

first you need to find them. if you have found them, walk over them to pick up them. then choose it from inventory and press fire (default mouse1 or mouse_left) button to throw them without delay. if you want to delay the throw just hold the fire key, but beware, they explode after 3 seconds. so if you hold it for more than 3 seconds, it will not explode in you hand, but instantly as you throw it- blowing up your face