Installing a window is simple if you follow these steps. When installing a new window, you should fold the nailing fins and place the sill into the rough opening. Next, place the window frame into the opening and push it into the framing until it fits squarely. If it's not square, use a level to ensure proper alignment of the window. If the windows are not square, contact the manufacturer of the windows to learn how to install them properly.
First, install shims. These shims will help prevent the window frame from bowing. Then, use a utility knife to trim them. Fill any gaps between the casing and the window frame with elastomeric caulk. If the gaps are larger than 1/4 inch, you can stuff them with foam-rubber backer rod. You can also fill any remaining gaps inside the window frame with minimally expanding foam. Finally, paint or stain the interior window frame to make it look great.