The FreeDB.org searching is based on algorithm for CDs. ID3 renamer compute this number from MP3 files. So you must mave the whole album, sorted in directory as tracks on album and the track must be in right length, else the FreeDB database will not be able to find the requested album.
The "View album info" button will show you the extended information about the selected album, eq. track names.
The "DiscID manually" button is used to load album, if you don't match any (eq. your album is incomplete or files length mismatch). You will be asked for FreeDB IDs (and the FreeDB Search page will be opened, where you find this IDs) and the album will be load.
If you have more files in the directory, the fields will be filled only on matching files, next files will be filled only with Artist, Album, Year, Genre properties.
With this option you can select the local FreeDB file (some CD rippers are saving these files) and use it for writing the information from it to the tag, like the FreeDB search.