Background Masking & composting Still Image Render

Hey Guys,

Im not entirely sure as to what the technical name for what im trying to do is called. so im finding it difficult to find tutorials with what i need:

im trying to insert my models into the vehicle that ive photographed. i need to mask part of the car seat so that my model appears in the correct position.
i need to add the background image at the same co-ordinates onto the Rectangle object so that it appears as part of the background.

i started using this tutorial

i think its out of date, He mentions a feature called “add sticky” i cant find that function. so im assuming that its now called something else.

grateful for any help, even if its just the correct terminology.