Starter shelving includes two side panels while Adder shelving has only one. Use a Starter section to begin each row of shelving, using the intermediate side panel to attach additional Adder sections to complete the row.
In addition, if choosing front angle posts on your shelving, adder sections will include two front posts as seen in the diagram. If choosing beaded front posts, adder sections will include one front post, as additional sections shares a common post.