butter_beer_drinker -

<strong> is like <b>, which bolds the text.
<em> is like <i>, which italicizes the text.
<br /> is like <br>, which causes a break in the line.
<strike> creates a strikethrough.
<a> should be <a href> which creates a link in the next.
<hr> creates a line from one end of the page to the other. Most authors use this as an indication of a shift in time/place/perspective
<p> creates two breaks so that a blank line forms between two paragraph
<ul> is similar to the list function on the site.
<li> is similar to the[*] in the list function and creates bullets for the list.
<ol> is similar to the[*] in the list function but creates numbers for the list.
<div> creates a header for a section of text.

You may find a better explanation if you Google each tag.