If you intend to use the greenhouse for ground level plants and large pot plants on the floor you will not need staging. For most people staging (The wide shelving at waist height) and shelving (smaller width shelves at shoulder height or above) are a must. Staging provides a surface at a useful height and makes potting, watering, pricking out and all the other greenhouse tasks much easier.
It also brings the plants closer to the glass and light. Smaller shelving provides additional space for placing plants.
Staging and shelving generally comes in Aluminium or wood. it can be slatted, smooth, have a raised edge. the aluminium can be powder coated to the same colour as the greenhouse frame. It can be afixed directly to the greenhouse frame or be free standing, and in some cases folds away so that, when not in use, it can be moved and the space used for plants from the floor up.
The most usual combination in a standard greenhouse is to have one side of staging and shelving, leaving the other side clear for grow bags, typically growing tomatoes and cucumbers.