Paragraph development by process involves a straightforward step-by-step description. Those of you in the sciences will recognise it as the formula followed in the "method" section of a lab experiment. Process description often follows a chronological sequence:

The first point to establish is the grip of the hand on the rod. This should be about half-way up the cork handle, absolutely firm and solid, but not tense or rigid. All four fingers are curved around the handle, the little finger, third finger and middle finger contributing most of the firmness by pressing the cork solidly into the fleshy part of the palm, near the heel of the hand. The forefinger supports and steadies the grip but supplies its own firmness against the thumb, which should be along the upper side of the handle and somewhere near the top of the grip. (from Roderick Haig-Brown, "Fly Casting")

The topic sentence establishes that the author will use this paragraph to describe the process of establishing the "grip of the hand on the rod," and this is exactly what he does, point by point, with little abstraction.