Meta Tags Are simple Html Coding To give more Details about keywords,title,description to googlebot.
these three meta tags are very important.when google robot come to our site.it will read it.there are some more meta tags are there, they are called as duplin core.Write Meta tag is one of the efficient task.because.there are some rules and regulations are there like
     1. keywords should be in 180 characters with space,no repeating.
     2.Title should be in 60 characters with space.
     3.description should be in 160 characters space.

Format for Meta tags  are:

1.<title>Title Name</title>

2.<META name="description" content="a description of your page">
3.<META name="keywords" content="a, list, of, keywords">

Other Meta tags Are :

1. Creator
2. Subject
3. Description
4. Publisher
5. Contributor
6. Date
7. Type
8. Format
9. Identifier
10. Source
11. Language
12. Relation
13. Coverage
14. Rights.

To learn more..http://en.wikipedia.org/wiki/Dublin_Core ,http://www.philb.com/metatag.htm,
http://www.metatags.org/