That's funny, I just added a summary to one of my Hubs, and saw your question. That means that you have to add a small summary of perhaps one sentence explaining in a nut shell what your Hub is briefly about. How you do it you may ask? Well you go to Edit your Hub. Then on the right hand side, towards the lower bottom you will see "summary", click on that. Then a space should appear where you can write your explaination. Once you are done. You can click done editing, and whalla the little gray A should dissapper.