Electronic components are either mounted directly on to the surface of a printed circuit board(surface mount or SMT) or have legs that go through holes drilled in the circuit board (through hole or TH). A surface mount to through hole adapter board allows you to use one kind of component on the other kind of board.
SMT to through hole adapter boards are mostly used in the prototyping of projects before any mass programming or assembly. They facilitate the testing and modification of a circuit or device, allowing you to go debug and fix any issues with your prototype.
SMT to through hole adapter boards come in different sizes depending on your needs, and can be single or double sided. Some have pre-scored break lines to allow for the separation of individual modules from the board as a whole.