wally

Hi everyone : I am very new to paint.net. Im trying to create a chroma green screen on an imported photo of a lap top. The lap top image screen is on a angle and requires an oblique rectangular shape and then bucket filled with a green color. The main rectangular tool always maintains its ratio and you cannot independantly move one side or skew one side of the rectangle. Also i cannot find a triangular tool ??? Can anyone help this first time user Many thanks inadvance