If you are planning to put Storm windows over your existing window there is a good procedure and a bad procedure. I want to tell you the good procedure then you can do the bad procedure if you don't agree.

The first step in any project is the measuring. Storm windows come in a variety of sizes. If you have standard windows you will be able to find matching storm windows. If you are covering windows that are of an odd size due to construction restraints you may need help.

You have two choices here, use windows that cover but don't fit exactly or special order ones to fit. The first is the less expensive method. i was able to purchase mine on sale and since i plan to remove them in summer i used a little over sized.

When you measure the window make two measurements, one is the inside area to be covered and the second is the outside area available. The inside area has to be right so that you can open and close the window. The outside area has to be able to fit the space between windows.

If you look at the photo you can see in my project the different sizes and the small space between each window. this required the windows to over lap and the holes that were pre drilled did not match up.

if you plan to leave the windows up full time then you should run a line of chaulking around the area where the windows are fastened, This will seal out the rain and keep bugs from entering. also be sure to remove any stickers that the manufacturer may have put on the windows. if the windows are dirty now would be the best time to wash them as well.

Start with a side that is nearest to the house. make certain that the window is level on top and on the side. Using the screws provided put the top screws in first then the side that will not be over lapped. I had to over lap the sides so once I hung the first one  put the second up using only the top screws. Then I drilled holes through the sides that over lapped and used a little longer screw. The last window only had to be drilled on the right side.

I repeated the procedure for the left side and then the front. I was able to do the project without help, but it goes faster ans easier if you have a helper to hold the window in place while you do the screws.

Good luck.