Why dllimport and dllexport needed while creating DLL files with C++?

I'm learning how to create dynamic and static libraries with C++, and my question is which way i should use when creating DLLs with C++. When i looked up to internet some people used something like __declspec(dllexport) while creating DLL files. But i tried to create dll files without adding this specification and it really worked well. Should i add this specification to my code ? (I am using windows 11 with gcc 12.2.0)