For review, here is a link to a listing of several posts on this blog related to worm feeding that you can review- what to feed, how to feed, and what NOT to feed.
Basically, any organic material that hasn't been tainted with anything poisonous substances, that is suitably rendered for ease of eating (ground and/or partially decomposed), and that is moist but not soggy. There are some foods you should avoid putting in your worm beds, such as potatoes, onions, meats, dog/cat feces. This post these and other foods to avoid feed worms (click for link). It is wise to take note, since you risk killing or sickening your worms by feeding them.
There are of course commercially prepared worm feeds such as "FRM Cricket and Worm Feed", If you have access to manures (horse, cow, rabbit, goat) and other organic material, it shouldn't be necessary to purchase these foods, or only use them for fattening up your worms to bait size.
Worm feeding is fundamentally important to successful worm farming. And you should never stop learning about.
Worm Feeding How-To's
For information and answers to your worm feeding questions, click here for a preview of my worm farming manual.