"Will call" is actually the LOCATION where you obtain the ticket. At a theater, it's part of the "box office." At the box office, there are one or more stations where you can buy tickets. At the "will call" station, there is usually one line, with a sign that says "will call." it's always shorter than the other lines, and so is faster than buying it at the box office.
"Primary will call name" means you must list the name of the person (the "primary name") who will be picking up the tickets at "will call." I like ordering on-line, picking my tickets up at will call, then going in ahead of all the people who are buying the tickets right before the show!
Hope this helps. :-)