Can't get rid of a web page?

[Richard]

So I visited a web page. Then another web page popped up.

I could not navigate away from the web page. Instead it offered me a dialog box asked me if I wanted to move off the web page. I know from experience not to click on those dialog boxes.

So I tried to kill the task in task manager. Whenever I tried to restart my web browser it went right to the web page. So I shut down the PC. When I restarted my PC and opened the web browser. Again, they web page appeared. I kept shutting down and restarting my PC until it went away.

My question is how do I deal with this situation in the future.