Your formula is comparing the column Locations in the table restaurants, with Thisrow’s cell restaurant. Comparing a column with a cell will not work.
Also, you have two Burger Kings in your locations table - there is no way for Coda to know which of those rows to use to pick an address. You need to have unique entries in Restaurant column, and then in your Orders table you need to use the exact reataurant.
Then try Locations.filter(restaurant=thisrow.Restaurant).store Address.
Which in English is something like, go to table Locations, goto the column restaurant, and find the restaurant that is the same as the restaurant in this row, and bring me the value in Store address.
The Orders table column “Store Address” is a Lookup column to look up the Store Address for the Locations table.
So in the only order #1001, the user is selecting the Restaurant Burger King and by doing so the Store Address Lookup column should show only addresses that match Burger King.
When clicking the dropdown in the Store Address column of the Orders table the addresses that match Burger King would appear in the filtered list.
The list should contain 100 Whopper Lane and 200 Whopper Lane since those are the two addresses that match Burger King in the Locations table. The address for McDonalds would not appear.