Feeding Zebra Danios
Danios are omnivores, and their diet should consist of a staple flake or pellet food with an occasional treat like freeze-dried bloodworms.
Brands of Fish Food
TetraMin is extremely easy to find and makes a good staple food. I like to feed my danios Omega One Tropical Flakes and New Life Spectrum Freshwater Flakes, though these brands are both a little more difficult to find in chain stores (any local fish store will carry them, though, and possibly Omega One). For any freeze-dried food, I like San Francisco Bay brand.
Flakes vs. Pellets
Pellets have the advantage that it's much easier to dose the same amount, and you also dramatically cut down on uneaten food polluting the tank. You might to consider Hikari Micro Pellets...just make sure any pellet food isn't too large, as danios aren't exactly adult cichlids...their mouths cannot handle large pellets.
Another thing to keep in mind is the fact that fish stores generally keep their fish on flake food, so that is what your danios likely will be used to, and what they're most likely to accept at first.
Feeding Frequency
There is no standard guideline for how often or how much to feed your fish. You really should only feed them what they can eat in 2 minutes, as excess food will degrade water quality. You will get a feel for it as you care for your danios...some people prefer to feed little amounts twice a day, some more than that once a day, some feed a conservative amount 6 days per week and then skip the 7th day to avoid constipation (yes, fish can get constipated...one way to treat this if they ever do is to serve them a blanched pea).