Okay, imagine you have some rules that you need to follow in your house, like not eating all the cookies at once or cleaning your room before you can watch TV.
In Islam, there are also lots of rules that people have to follow, like praying five times a day or not eating pork. A jurist is someone who studies these rules and tries to understand them better.
An Islamic jurist is specifically someone who studies the rules in Islam, known as Shariah, and helps people understand how to follow them. They use big books called "Hadith" and "Quran" to learn about the rules and make sure people are following them correctly.
Think of them like the boss of the rules. They have to make sure people are following them and explain them to others who might not understand. Just like a teacher or a parent who has to explain the rules to you, the Islamic jurist has to explain the rules of Islam to others.