To add files to the Media Library click on Dashboard and select Media.
To view files you can click on a folder or view all files. If you want to upload a file you can do it directly to a folder if you wish.
Note that images should be in jpeg format. Files for adding to documents should be in pdf format. You can sort which images you view, etc., by selecting the appropriate box.
Once the files have been uploaded you can add to Galleries or to Posts, or to documents, if you have permission to do so. All Members can create posts once they are logged in.