Computers are not that simple.
There is no such thing as a camera ON anf OFF switch or button on the computer.
It s all controlled by SOFTWARE or PROGRAMS.
When you OPEN a program that controls your cam, such as skype, or other cam software, then the came can be accessed.
Also, each website is built differently, and there is no way to know if the website YOU ARE GOING to will be nefarious, or safe.
As you can imagine, all parts on your computer can be accessed using SPY software, and you would not even know it.
So, your question does NOT have a simple answer.....but to be safe.....I would advise useing a sticky note to cover the webcam if you are worried about it. That is the ONLY 100% sure way to keep anybody from seeing through your cam.