You use the map, which sits in the corner of your screen, to switch between the places you need to perform tasks. You start each day in the back room, where you have to complete all your work before you can move into your assigned department.
I played through five workdays in the game, and in that time, the only locations that I needed to toggle between were the back room and the grocery section — so the floor plan seems kind of unnecessary. Walmart's spokesperson says that developers are in the process of adding a new level to the game that would take place in the "lawn and garden" section of the store.
If they really want to put the floor plan to good use though, Walmart's developers should consider adding a "Battle Royale" mode.