Since it is a kind of fast food, there is a cooking station inside counter. Customer would stand outside and order type of udon they want. After staff prepared and sent to customer an udon bowl, custotmer would have a chance to add on (by yourself) -- neghi, even oden, sauce at the spot.
If walking further, there's a shelf with 2 levels of many types of tempura (deep fried battered vegatables or seafood) and kakiage (tempura made up of small shimps, dried cuttlefish, or scallop ...). Here's the final point for customer to add anything it before reaching payment spot.