The "staff" of a business is the collection of people that work there. Offices, shops, and schools all have 'staff'.

The phrase "shop staff" means the salespeople, cashiers, and other people who work at a store.

"Staff" is a tricky word because it can be either singular or plural:

Their staff is extremely helpful.

The staff went out to an Irish pub for their holiday party.

If you want to talk about just one person on the staff, you can use the phrase "staff member".