In Judaism, dietary laws are a function of the Torah, from the section of the Old Testament known as Leviticus, as well as from a few other sections, such as Exodus. These laws are considered to be an obligation of the Jewish faith, and they are meaningful because they are a way of carrying on a religion over 5,000 years old and a way of maintaining a distinction from other faiths.  There are many dietary laws, but I will mention those that many consider to be most central to Judaism. All of these, collectively, are referred to as being "kosher." 

First, because of a prohibition in Leviticus, that one may not "cook a kind in its mother's milk," one may not combine meat and milk products in cooking or in eating.  After a meal that includes dairy products, one must wait three or four hours before having a meal that includes meat products, and if one has a meal that includes meat products, there is a longer waiting period.  It would appear that there was some understanding, even early on, that it takes longer to digest meat than it does to digest a dairy product.  This prohibition means avoiding many foods such as cheeseburgers or any meat cooked in a white sauce.  Anything that is not meat or dairy is considered "neutral," so that fruits and vegetables, for example, may be had with meat or dairy. 

Second, a number of different kinds of meat and fish are prohibited in Leviticus, including shellfish, animals without cloven hooves, and the rear portions of a cow.  Horse, deer, and pigs are forbidden, for example, as are shrimp, crabs, and lobsters. 

Third, all meat that is permitted must be "perfect," in cleanliness and without any diseases or sores.  It must be slaughtered in a particular way, in a humane manner, and a rabbi must supervise the slaughtering to make sure the animal is fine and is slaughtered properly. 

There is much discussion about how these particular laws arose, some speculating that because of primitive cooking utensils, people could have begun to realize that meat could contaminate a dairy dish, or vice versa.  The forbidden animals might have carried more diseases than the permitted animals.  However, even if there were good reasons for these laws, the fact is that they are obeyed for religious reasons, rather than for practical ones.

Generally speaking, Jewish people also say blessings over the food they are about to eat, for example, over their bread, their vegetables, and their wine.  These prayers are often said in Hebrew, but I do not think that Judaism differs all that much in this regard, since in many religions, blessings are said over food.

There are probably as many Jewish food traditions from a cultural perspective as there are countries.  In all countries in which there has been a Jewish presence, the local food customs have permeated Jewish culture.  My own ancestors were from Russia, so my father was fond of borscht, a beet soup. Spanish Jews, German Jews, and Moroccan Jews have food traditions that reflect their local culture and adapt to obey the dietary laws, too.