The main program needs a reference to the DLL. If you build the main program in the same project group as the DLL project, open the Project menu, select References, and check the DLL project's entry.
If the main program is in its own project, load the DLL project, open the File menu, and select the Make Xxx.dll command to build the DLL. Then load the main project, open the Project menu, select References, and check the DLL's entry. If you cannot find the DLL, click the Browse button to select it.
After you have created the reference to the DLL, you can create an instance of the class and use it's public GetIcon method to retrieve the pictures stored in the DLL.