A group of sentences in written material typically separated from other groups by typographic means.
You know what a paragraph is, of course. Notice that the definition describes the functional role of a paragraph but does not describe how a paragraph is displayed. In HTML a paragraph is placed between these two tags:
<p> paragraph goes here </p>
To be compatible with HTML version 4.0 use small letter "p". Most browsers will also let you use a capital "P" but this is a deprecated feature. You don't have to start the tag in column one. Here is a small web page containing a single paragraph (and some other necessary tags which we will get to in a moment):