The meta title tag - This tag is very important for indexing.
Google uses the title tag for indexing so you should include some of your keywords. Google also uses this tag for the title it displays in the SERP for your page, so you should make it something human friendly to attract visitors. Don't make it too spammy.
The meta description tag - This tag is very important for getting your site niticed in the SERP.
Google does not use the description tag for indexing. Google uses this tag for the excerpt it displays for your listing in the SERP. You should write the description with the human visitor in mind, this is your chance to get them to click on your link instead of one of the others in the SERP.
The meta keyword tag - This tag is only important if your using adsense or similar program.
Google does not use the keyword tag for indexing. It does use it for selecting relevant ads for adwords, so if you have an adsense site you need it. Otherwise the main use is for the very few SE that still look at it, and more importantly a place for you to keep track of the keywords your targetting for yourself. If you haven't looked at a site in awhile, its a good reminder of what you were doing with it.
The meta keyword tag was an idea put forth many years ago, but only a few search engines used it. Google never made use the keyword tag for indexing.It became apparent almost immediately that webmasters couldn't be trusted to use it correctly. Keyword spamming in the tag was the immediate effect. Even the few SE that used it initially no longer use it.
Having said that, there are many people that continue swearing by the meta keyword tag. Rather than debate the issue, I suggest you go ahead and use the tag. If they are right then it might help, if they are wrong (as most documentation and researches suggest) it still won't hurt to use it. If you do use it use it correctly, don't try keyword stuffing.
Keywords ARE very important to SEO. Don't misunderstand me, keywords are probably the most important thing after backlinks. But it's their use throughout your page that makes them relevant. Proper use of the header tags (H1,H2,etc) are very important. Keeping a keyword density of about 1.5-2% in your content is important. Using keywords in the alt and title for your href and img tags is important.
You can read this other thread to find additional suggestions and external references supporting these claims.
http://www.blackhatworld.com/blackh...73-stop-stressing-over-keywords-meta-tag.html
