Feeding is the most important (and easiest) part of keeping up an aquarium (feed the fish, not the aquarium!).  All that you need to know is what type of food and how much.  Most fish will eat regular flake food that is sold at all local fish stores (lfs).  To feed fish flakes, you may need to break them up some so that they can be eaten easily if the fish has a small mouth.  Otherwise, put them in whole.  Other fish need special foods.  goldfish, cichlids, and plecostomus are examples of these fish.  Some large fish, like Piranhas need live fish like small goldfish, danios, or minnows.  Small fish fry (babies) need brine shrimp, which you get as eggs and hatch.  Plecos need an algae chip few nights a week.  It is also good to skip a day every 3 days (feed 3 days, skip a day), or feed every other day.

    There are other special things you should think about when feeding.  You should try to offer different foods on a rotating schedule.  Most or all fish like life food, and brine shrimp are easy to hatch.  There are also many types of freeze dried and frozen foods that fish will enjoy as weekly treats.  On vacation, you can skip a week without feeding, or you can leave a small amount of food in a pill box for someone to come by your house to give to them (make sure you put only the amount to feed the fish in the pill box, and have more pill boxes for other days).

    Once a week, you will probably need to clean the aquarium.  Really, this is extremely easy.  You will need some type of a gravel vacuum to syphon out 25 – 50% of the water at the same time.  You need to vacuum the gravel if any food that fell past the fish (a sign of over feeding).  If you have a pleco, goldfish, or cichlid you may have a large mess to clean up, but with a good filter system,  it will be easier.  If you don't have a pleco or otto, you may need to scrub algae off the glass.

    You should also clean the filter every month, unless you only have an undergravel filter.  I don't suggest completely replacing a filter cartridge unless it is torn up.  The cartridge is where many bacteria live in the tank, and it is very important to keep them in the filter.  If the cartridge has carbon in it, cut a slit into the cartridge and throw the carbon in the trash (it quits working after a week or two, and isn't needed most of the time).

    For an undergravel filter, it is a good idea to syphon the junk out by running a tube down the lift tubes and moving it around.  You should also vacuum the gravel as well as possible.  But when you have taken out the amount of water you want to change, quit vacuuming.  Just start back where you quit next time.  UGFs are very hard to keep clean because so much junk accumulates under them.  They have, however, shown their usefulness for several decades.