In order for fish to be kosher, Jewish law stipulates that it must have both fins and scales. No specific ritual is necessary for slaughtering fish. Shellfish and mammalian fish are not kosher, since they do not have fins and scales. The other essential aspect of keeping kosher is the prohibition against mixing milk and meat. Milk represents birth and life sustenance.
Meat stands for flesh and death.
Mixing them shows an insensitivity to life. Using these three citations, the rabbis, in later discussions, deduce three meanings for the prohibition on mixing milk and meat. Current opinions on how long one must wait after eating meat and before eating milk vary, ranging from the Dutch practice of waiting for one hour to an Eastern European custom of waiting six hours. There are thousands upon thousands who already incorporate kashrut into their daily lives. You can start by looking for foods with a mark of kosher certification known as a hekhsher.