If I understand correctly, you have a music library on your computer that is separate from your iTunes library. You want to add the albums from your separate music library to your iTunes library.
(1) If that is what you are trying to do, and if searching for the topic via your Mac's iTunes > Help menu command does not show the information you need, you will find help in the "Add to Library" section in this article: http://support.apple.com/kb/HT1347
(2) If, instead moving albums between libraries, you are trying to move music between devices, pick the appropriate topic(s) from here: http://www.apple.com/support/itunes/media/
Steve MacGuire aka turingtest2 - iTunes & iPod Hints & Tips - Grouping Tracks Into Albums - http://www.samsoft.org.uk/iTunes/grouping.asp (older post on Apple Discussions http://discussions.apple.com/message/9910895)
Quick answer: Select all the tracks on the album, File > get info, and either give them all a single "album artist", or check the "compilation" flag (as in https://discussions.apple.com/message/17670085).
If these are from multiple-CD sets you may also need to enter the appropriate information in the disc number fields.