Cut 5 inch strips of flashing that are 2 inches taller than the window and will overlap the bottom flashing by 2 inches.
How to install vinyl siding trim around window.
Install the flashing from the bottom up.
Cutting and installing the siding 1 place the piece of siding to be installed under the window along the bottom edge and hold it where it will be located horizontally along the wall.
The 5 inch wide flashing should slide right under the nailing fin on the window.
Install the tops first then the sides and then the bottoms of the window surrounds.