Thanks to sparks4289 for clarifications.
EDIT: If any of you care to see my website, it is at http://220.127.116.11/index.html. It is not quite done yet! By the way, the login scripts on the page are made of the PHP and MySQL from Wampserver, just to show it works.
Step 1: 2. Preparations
Log into your routers web page (this is usually http://18.104.22.168)
Find both your real IP(What everyone else uses) and your local IP(only you use this one). Be sure to write both of these numbers down.
Step 2: 2. Download the Server Program
Step 3: 3. Write the Website's Code
NOTE: This can take a while even if you are skilled in PHP/HTML. Don't expect it to be easy.
Step 4: 4. Put Online!
EDIT: In some cases, you will not have a 'static' IP address. This means that your IP will change every time you go online. In this case, you may need to pay your ISP for a static one.
CONGRATULATIONS! You now have a fully functional website!