How to add another folder

I have created a library and have one folder in it but i am not able to add another

You can add a new folder using +, or drag & drop, to add comics to a new folde you can use drag&drop. But I normally handle the structure using File Explorer and then I update the whole library, the app will add anything that's new in the hard disk.

When i selct + that just makes a new folder which does not have any files in it and i dont know how to add the comic files to it

How to do i add the files to the new folder created. My files are in a folder and when i tried to import them it was said they dont contain any library

I just told you, drag the files into the folder. But my recomendation is to copy the files normally using File Explorer and then update the library, the default shorcut is U.

If your library is in C:\MyComics, add a folder with comics like C:\MyComics\NewFolder, NewFolder contains the new comics you want to add to the library, then go back to YACReaderLibrary and press U (this is the default shortcut for updating the library).