In the frame of the dialog, you are able to set which users are allowed to access your FTP server. You can grant access only for anonymous users, only for authenticated users with accounts on the system or for both types of users.
If you want to allow users to upload files to the FTP server, check in the frame of the dialog. Here you are able to allow uploading or creating directories even for anonymous users by checking the respective box.
NOTE: If a vsftpd server is used and you want anonymous users to be able to upload files or create directories, a subdirectory with writing permissions for all users has to be created in this directory.