Measure the window opening
Buy a screen frame kit or pre-made screen
Cut the frame pieces to size if needed
Assemble the screen frame
Cut the screen mesh larger than the frame
Lay the mesh over the frame
Press the spline into the frame groove with a spline roller
Trim the excess mesh with a utility knife
Install the screen into the window opening
Secure it with screen clips, tabs, or springs if required
Check that the screen fits snugly and opens or closes properly