Select the Add Files button on the top right of your bookshelf.
Once selected, this button will allow you to add files to the library. Your computers File Manager will open, from where you can select files to be added to the Library.
There are several ways to add files
1. Select the file to add and then click on the Open button in your File Manager.
2. Select the file and drag it over to the library bookcase.
3. Select several files and repeat either step 1 or 2.