At risk of repeating myself from another thread, but for completeness....
Attributes can be edited/created both manually and via the UpdateMedia script that runs regularly. UpdateMedia will pull id3 tags in from mp3s and write them into the database. So using an id3 tag editor or just the file properties in Windows, you can quickly set all the tags you want and LMCE will pull them all in for you automatically.
Only problem is, UpdateMedia only looks at embedded tags in audio files like mp3s. Video is creates a separate file as not all container formats support embedded tags. So unless you can create these .id3 tags its gonna be hard to use this method for video....