How do I design a video conferencing site?

Well since you don't have any idea where to start. You need to learn HTML/CSS. Then you need to learn how you can integrate java into a website/what framework you might want to use, for example Spring MVC. Then figure out how to connect a web camera to your website and allow access to it.

In order to tackle something like this and not feel so overwhelmed that you have no idea where to start, you need to break the problem into smaller pieces. Then start to tackle small pieces, pretty soon you'll start having small victories and next thing you know you'll have implemented half your functionality. Also, remember that programming requires critical thinking...simply googling for video conferencing site in java may not reveal a one size fits all solution...you are going to have to do some of the leg work to get your project off the ground and functional.

Now if you start your project and have real code issues where you are stuck, feel free to come back with a clear explanation of your issue, some relevant code samples and I'm sure someone here would be happy to help.