Imagine you are playing a game with some friends, but there are no instructions on how to play. So, you ask your friend who knows the game really well, and they tell you how to play it. This is similar to what "oral law" means.
Oral law refers to religious law or tradition which is passed down by word of mouth, rather than being written down in a book or written document. It is a set of rules and teachings that are not found in the official religious texts, like the Torah or the Bible.
The idea is that these teachings were passed down from generation to generation, from the time of Moses, without being written down. These teachings include explanations of how to follow religious law and traditions, as well as interpretations and commentary on the religious texts.
For example, in the Jewish tradition, the rabbis of the Talmud, a big book of Jewish law, discussed and debated many religious laws and customs that were not written down in the Torah. These teachings were passed from teacher to student orally, and they continue to be passed down in Jewish communities to this day.
In short, oral law is a set of teachings and customs that are not written down, but are passed down through the generations by word of mouth. Its aim is to explain and interpret religious texts and offer guidance in following religious law and traditions.