A good pellet brand should always serve as your staple diet, though variety, just like with any animal, is key to a great over-all diet. ;)
Frozen foods generally come in little cubes(though some come in sheets you can brake small pieces off of)so what you'll want to do is take a knife and scrape off/cut a small piece from the cube and place it in a small, clean container(bottle caps work well, just rinse them well in hot water before using), add a couple drops of tank water, wait for it to thaw, then feed. ;)
It'll take you a couple of times to figure out how much to feed....I usually stop when my boys start to sport a tad bit of a belly, which only takes a few worms/shrimp. If you happen to have extra though, don't re-freeze it, just toss it.