The P tag is one of the most commonly used tags, but it isn't normally used as shown in the HTML specification. Many users simply add P tag to add a break between paragraphs. As follows:

This text is in paragraph 1.
<p>
This text is in paragraph 2.

The specification uses an ending paragraph tag, as follows

<p>
This text is in paragraph 1.
</p>

<p>
This text is in paragraph 2.
</p>

Because the second example follows the specifications, you should use that format instead of the first example. While browsers will probably always support the first method, the second format has an extra options unavailable in the first. You can add the ALIGN parameter and specify LEFT, RIGHT, or CENTER. An example of the ALIGN parameter follows:

<center>
This text is centered
</center>

<p ALIGN=CENTER>
The first text is also centered
</p>

<-- Back to CENTER Tag -- Next to BR Tag -->