Guides are official volunteers who help players and run small events on servers. To find out more about the Guide Program you can visit https://guide.station.sony.com/guideapp/faq.php and should you wish to join the ranks of the program simple fill out the Guide Application located at https://guide.station.sony.com/guideapp/.
Some items in the game are only available via Guide Quests. On the Test, Freeport and Live Exchange servers there are no Guides, so NPCs give quests for these items. See also: Category:EQ2 Guide Quest Rewards
You can see if your server might be having an guide event soon by checking the Guide and Player Events Forum on the official EQII Forums.
See also: Category:EQ2 Guide Quest Rewards