Foreshortening in art refers to the way we perceive an object as it recedes in space. It is typically only used to describe more extreme angles. Objects appear to get smaller as they recede into the distance, it looks shorter or more compressed than they actually are.
Objects at the front will overlap objects behind. Although the effects of foreshortening could be determined with absolute certainty through mathematics, it does not need to be perfect, it just need to be convincing.
Use overlapping shapes, edges and cross contours to show the volume of an object. Imagine the object is transparent. Drawing the mass will help to better understand the volume of the object and how it is positioned in space.