This question is about your ability to self-assign a shop.
New shoppers (to the iSS system) have no history and in the beginning, may only self-assign one shop at a time. As your history expands by completing shops through the system, your Agent Rank climbs and you are able to self-assign more shops at once.
PLEASE NOTE: A scheduler can always assign you more than one at a time - and you may request as many as you'd like. This restriction only pertains to self-assigning. So if there are more shops you are interested in than you are able to self-assign, please contact the scheduler directly and ask if they can give you more.
As your Agent Rank climbs, so does the number of shops you may take without a scheduler involved.