When registering, simply enter APC as your company name, as that is a required field. The employee count doesn’t matter, but it is 500+ if you care to enter that info.
When registering, you will have the option to have an in-store card sent to you. If you don’t elect to do so but later want to use the discount in-store, simply login and go to your profile, where there’s the option to print a card. Without a card, you can’t get any in-store discounts.