JDK (short for Java Development Kit) is a tool from Oracle Corporation for developing Java applications.
Since our course uses Java to solve practical tasks, you will need to install this tool.
You can download the developer kit on the official website of Oracle or from here
https://jdk.java.net/20/.
Detailed information about the JDK and its installation is described in this lecture of our course:
https://codegym.cc/quests/lectures/en.questsyntaxpro.level20.lecture00
P.S. When this video was edited, the current version was JDK 16. You do not need to search and download this particular version. You can download and install the latest JDK.