Locate the two parts of your storm window, which are called the outer sash and inner sash. The outer part of your storm window will be on the top, and the inner part of your storm window will be on the bottom. On the inner and outer sashes you will notice locking mechanisms on each part.
Clean your storm window's tracks. Remove all debris with a brush and scrub them with soap and water. This will ensure that the various parts of your storm window can slide easily, allowing you to close them properly.
Close the inner sash, which is the bottom, by sliding it the entire way down.
Slide the outer sash, which is on the top, into place. You will see that the outer sash should slightly overlap the inner sash. This is to prevent any water from gaining access to the underside of the storm window. If closed properly, water should slide off the outer sash.
Secure the upper and lower sashes together. There will be at least one lock, and usually there will be an inner and outer lock. These locks ensure that strong winds are unable to move your storm windows.