What is a DLL File?
DLL stands for Dynanic Linked Library. The whole point of dividing code into a DLL is for reusability. If you have a code that you know you will use over and over again, you can create that code as a DLL and use it in your app.
DLL’s need a host to run and do not run by themselves. The EXE file, the file where Main Program is in, is needed to host the DLL in order to run.
DLL’s are useful because they are reusable. You can build on other programmers code.