Summarize this article in one sentence.
Many Internet service providers (ISPs) expressly forbid personal hosting unless you have a business plan, which often costs significantly more than a standard use plan. This shouldn't be an issue if your site only generates a few hits per month, but any kind of significant traffic will draw attention to your hosting.  If your ISP prohibits home-hosting, either upgrade your plan to one that allows hosting or switch to a different ISP before you continue. Failing to heed your ISP's policy for home-hosting can result in anything from getting your Internet turned off to having to pay fines. In order to host a website, you must have a computer on and connected to the Internet 24 hours per day, seven days per week. This is easier to accomplish with a secondary, older computer than it is with your primary computer. Restarting your computer to update will occasionally be necessary. During these updates, your website will be inaccessible. Make sure that your computer is up-to-date with the latest operating system, security features, and drivers. Make sure you update your Windows computer or update your Mac computer before continuing. If your website's source code isn't already in a file on your computer, copy it from your web service's settings into a text document on your computer and save it as a PHP file.  If the website's source code is stored on your computer, make sure you know where to find it. If you haven't yet programmed your website, you'll need to do so before continuing. MAMP is a free website hosting application that works on both Windows and Mac machines. To download MAMP:  Go to https://www.mamp.info/en/. Click DOWNLOAD below the "Free" version. Click the orange Download button. Wait for the file to finish downloading.

Summary:
Make sure your Internet service contract allows hosting. Ensure that your equipment can handle hosting. Update your computer. Move your website's source code onto your computer. Download the MAMP program.