There the eggs hatch into a larval stage, and the larvae float freely and eat tiny plankton until they grow into fish. See the Moe reference for a more complete description. Parental care in the fish world varies widely. Parents can be anywhere on a continuum from eating all their eggs or fry, to both parents fiercely guarding their eggs and fry. Many fish parents show some common behaviors, so I will discuss them here.
Most fish consider any and all fish eggs and young to be a tasty treat.
Therefore most fish will not hesitate to snack on any they find, including their own. This means that egg scatters and many substrate spawners really cannot be bred in a community tank, as the eggs will quickly be eaten by the parents and other fish. Marine fish and invertebrates also eat eggs. Livebearers are especially notorious for eating their young. A few fish ignore their eggs or fry, and so can be bred in a species tank.