|Meta tags will not alter how your web page will view, but Meta tags will help search facilities index your site, and what each page has with in it. Just as the title tags tells us what the title of our page is, the meta tag tells what our page is about and some of the key words that will be found on this page.|
There are many different types of Meta tags besides the keyword and description tags, for instance there is author, page update, robots, language, etc.
Many people just make a template and use the keywords and site description for the index / main page, and every page made after that uses the exact same key words and description. This is wrong and it stops many of your pages from being indexed in the right category.
An example would be lets say you site is about dogs, your keywords and description is about your dog. Then on a page about veterinarians you use the same keywords that is not used in this page at all, this will cut your chances of having this page listed in that category. One way to increase your presence in the search engines is by keywords. And one way to add keywords to your site is to do it page by page, some keywords will be the same on page after page but others are page specific.
There is a web site, META TAG ANALYZER, that will assist you with this task, giving you an idea of how Meta tags should be incorporated. This helpful site is not the only one out there, but it is a good one that I have used. There is also a keyword analyzer there that I recommend using to in the development and/or review of your keywords meta tag.