There are many laws of kashrut—food proper for the Jewish people—in the Torah. In fact, they are scattered throughout different sections. Of course, the Shulchan Aruch—the code of Jewish law—is responsible for codifying and systematically organizing them.
This week's Torah portion discusses, among many other topics, some of the laws of kashrut. However, in addition to the well-known signs that animals (land animals, birds, and fish) must meet to be considered edible, there are laws that define how the animal must be prepared for consumption.
More specifically speaking, a verse from this parashah (Devarim 12:21) says: "When the place that God your Lord chose to make His presence dwell there is far from you, and you slaughter your cattle and your flocks that God gave you, as I commanded you, you may eat in your cities, as you wish.".
Our sages learned several concepts from this verse, including one directly related to kashrut. The verse states that when you slaughter an animal, you must do so "as I commanded you," meaning in a specific, previously transmitted manner. However, if we search the entire Torah, we will find no place where God explains how the slaughter should be performed for the meat to be considered kosher.
This is one of the places in the Torah where we can see that there are certain matters that are not entirely clear, and that some form of clarification is needed. And that form is called the Oral Torah.
There is a Written Torah, which consists of the 24 books of the Tanakh (the Bible), including the five books of Moses, plus an Oral Torah, comprised mainly of the Talmud and various Midrashim. However, one Torah without the other is incomplete; that is, the Written Torah is incomprehensible without the Oral Torah, and the Oral Torah lacks foundation without the Written Torah.
What's interesting about the verse mentioned is that it's one of the places where the Written Torah itself refers to the Oral Torah...
We must know that both were given by the same God, at the same time, in the same place, so both have absolute validity and authority over Jewish life in particular and over the universe in general, both are the will of the Creator, the guide to lead the world to its reason for being, to be a dwelling place for God.