How to reinstall Bootcamp on my Mac?

I know I had bootcamp installed onto my mac before I installed Windows but I guess within the process of me installing Windows, I deleted bootcamp. I'm now currently stuck in Windows and I can't go back to Mac OSX, and my laptop won't even connect to the internet (Windows keeps asking to connect to the internet but it won't even let me hook up to my own wi-fi). I'm out of ideas of what to do!