To caulk around a window, scrape off old caulking with a putty knife, and clean the surface of any remaining caulking. Prepare a caulking gun for use, place the tip of the gun on the edge between the window and the wall, and compress the handle of the caulking gun to produce a steady stream of caulk. Move the gun along the window until the entire perimeter is sealed with caulk.
When removing old caulking from the window, try to pry up the caulk line in one spot, and pull it out by hand. Use a wet cloth to wipe the area down.
To get a new caulking gun ready for use, press the release on its bottom, move the metal plunger outwards, and place the silicone caulk tube inside the hole in the caulking gun. Push the plunger on the bottom of the tube, position the release in a way that keeps the tube in place, and remove the tip of the caulk tube using a pair of scissors. Be careful not to cut off too much, as then the stream of caulk may be wide and difficult to work with. Use a metal wire to break the inner seal.
When caulking, try to keep the caulking gun at a 45 degree angle against the window at all times. Start caulking from the top part of the window, moving down to the bottom. Try to create an even line of caulk along the window.