It contains a brief introduction of your site which is placed within the content field of this tag. This description will be included when a search engine shows the results to a user which influnces whether he visits your site or not. This tag contains a list of all keywords relevant to your site. If your site is about yourself then the keywords can be personal, homepage, biodata, photos, family, about, me, myself and so on. Here's an example of keywords we could use for this tutorial.
Some browsers support keywords seperated by just spaces.
Most HTML tags occour in begin-end pairs. Also multiple tags can be used together. But the thing to watch out for is that the two or more different start-end pairs do not get tangled up or overlap. The innermost pair has to has to be closed before the next outer tag can be closed. This is also called nesting of tags as the tags are nested within each other.