The Hosts file is like an address book. When you type an address like www.cpwebhosting.net into your browser, the Hosts file is consulted to see if you have the IP address, or "telephone number," for the server that the site is hosted on. If you do, then your computer will "call it" and the site will open. If not, your computer will ask your ISP's (internet service provider) computer for the phone number before it will go to that site.
Step 1: Go to My Computer and click on your main hard drive(usually C:/)Step 2: Click on WINDOWS and then on system32
Step 3: Click on drivers and then etc
Step 4: Open up the Hosts file with notepad or another text editor
You can also use the HOSTS file to block ads. I.E. 0.0.0.0 advertisingsitethatyoudontwant.com If you google for HOST file lists, you can find premade HOSTS files with the majority of AD sites blocked already. I used this a long time ago (premade list) but it ended up blocking certain things I needed.