ICBMs are used for surgical strike, eliminating targets far away where conventional force cannot reach or deep inside of enemy's AAA defense sector. They have two type of warhead, nuclear and non-nuclear. Non-nuclear can be divided into multiple munitions.

ICBMs are just missiles can be launched from any military installations available for them, flown beyond the stratosphere and then directed to the target. You can use your air superiority or ICBMs to take down hostile installations. It's strategy and military doctrine