Should be used in conjunction with, not instead of, headers to separate the web page into sections. Just plain text is a bit boring, so HTML has built in some different text styles, a few of which I am going to show you. Teletype displays the text in a monospaced Courier font by default on most browsers. The elements can appear in any order. Browsers usually format this type of list with bullets or another type of marker.
Elements appear in a specific order, like steps in a process.
The browser will add numbers to each element in the list. Walk the dog.