Cats are strict carnivores and therefore get their nutrition from meat, but a lot of cheap supermarket food contains much maize, animal derivatives and 4% meat. Maize cannot be digested by cats and is just a filler in the food. Animal derivatives are a mixture of leftover meat e.g. ears and bone - it is also speculated to contain hair.
For a healthy and well feed cat food with high levels of meat such as Applaws, Natures Menu, James Wellbeloved, Lilly's Kitchen, Royal Canin and others.
Dry vs Wet food
There is a heavy debate over full dry and wet food diets. It is currently thought that a mixture of wet and dry food is the best for your cats teeth and to avoid urinary tract issues.