CDDB is a giant database (now actually owned by GraceNote). That and others like it (FreeDB) are what the media players use to identify a CD when you put it in the drive. Basically it calculates an id using the number and length of the tracks on the cd and that id is the key in the database to look up the details of the tracks (title, length, artist, etc).
ID3 is the 'tag' you were talking about. Version 1 tags are at the end of the file and are not used too much anymore because it doesn't work too well for streaming music (you have to read the whole file to get to the end where the tag is so you can't display the details of the track when it first starts playing). Version 2 (2.4 is the latest) tags are at the beginning of the file and may contain far more information than v1 tags.
There are many freeware and shareware apps that deal with tagging and renaming multiple mp3s at a time. Tag&Rename is one I remember that seems to work pretty well. Just google for 'id3 tag' and you will find them.
I personally don't use those tools because I do all of my music in SoundForge and I get it right the first time.
. But if you are getting files from alot of different sources and need to get the tags to be correct and consistent you are going to need a tool that can deal with multiple files at a time.