Projects are applications that you will develop from start to finish on your computer. In contrast to the course exercises, which focused primarily on evolving coding skills, the projects will give you hands-on experience in a real environment.
For most professions, the learning program includes 4 projects, each of which develops a particular area of programmer competence. It all starts with setting up the local environment and getting to know the basic developer tools and ends with creating full-fledged sites to be deployed on online platforms.
This all happens while learning is still ongoing - this way, new topics are learned much better and are reinforced through practice. Projects are the answer to "why do I need this?".
Each project becomes an addition to your portfolio. The source code is in your personal GitHub account, and you can show it to employers. A portfolio of completed projects is very important when hiring both experienced and novice developers. Many employers will look at GitHub first and only then at the classic resume.