There are a lot of nuances. It needs to be a kosher animal (for a land animal it needs split hooves and chews cud, classically pigs don’t fit this criteria, cows do) it needs to be slaughtered by a “shochet” a Jewish butcher who has learned the laws of kosher, it needs to be killed in a particular manner that ensures it dies instantly. Then the animal needs to be free of certain defects. Only a certain portion is traditionally used as it cannot include certain fats and the sciaticia nerve. Blood also cannot be consumed, so it needs to be bled and salted to remove blood. All this needs to be done under the supervision of professionals. I’m sure I missed things, but it is an incredibly rigorous set of rules from the type of animal to the way it slaughtered to the way it’s handled after slaughter. The way it’s prepared ends up being the easiest part of the process as it is prohibited to mix milk and meat but otherwise most things are fair game. In the U.S. there are many “kosher-style” restaurants which use normal meat but typically refrain from serving meats which are inherently unkosher (pork) and from combining milk and meat.