What is the purpose of Panels in java

I'm a high-school student who is taking java I usually don't have many problems that I cant figure out without a bit of research however my teacher insists all student use panels when building GUI's.I have no problem building them however I haven't been able to get a decent answer clarifying the purpose of putting components in a Panel

Solution

A panel is a container.

It allows you to group components together
It allows you to devise complex interfaces, as each panel can have a different layout, allowing you to leverage the power of different layout managers.
It allows you to build reusable components and isolate responsibility
But most of all, it gives you the bases for deciding how the panel should be deployed. With a panel you can add it to a frame or applet or another component as needed...
A panel also makes a good surface onto which to perform custom painting. For all the benefits mentioned above - its isolated and reusable...

There are many other reasons for using panels, these are just a few that pop to mind