DAL and BLL are design ideas. It can be in the form of two classes, two folders, two projects... whatever.
Right-click the solution (or file) → Add → New Project → Class Library (can be DAL or BLL).
BLL calls DAL, add using DAL at the top in every class file of BLL. Expand the class library: right-click Reference→Add Reference→Project-Find the newly created DAL.