Sometimes there are URLs which point to images. While it's easy to just
<img src="URL" />
in HTML, there are cases where this is not possible, or will not work.
GitHub's a great tool to maintain your code, but it's definitely a little confusing the first time around (and, possibly, a few times after that). Here is a quick guide on how to use it efficiently.
In many situations you want to download a file (or a page) from another server to your server. You can do this with cURL! Here is a function which does that, written in PHP.