Meta tags are pieces of information placed in the code of a web page and are used by search engines.
Keywords - any word or phrase an Internet user might search for in order to find a website or a page. You should limit this to around 150 characters, roughly 20 words.
Also consider the potential level of competition your keywords will have. For example, website designer will return many millions of results but Website Designer Hull will greatly narrow the search. The Google Keyword Tool will show the approximate search volume for your keywords and help suggest possible alternatives.
Keywords are also used in many other areas across your website. Be sure to check out the Search Engine Optimisation page.
Description - this is the information that is displayed immediately after the main link on many search engine results so it should be a brief and concise summary of your page's content. You should aim for around 20 or 30 words. A reasonable guide would be a paragraph of text or a couple of short sentences.
You can set default meta tags by clicking the 'Default Meta Tags' link at the top of your admin pages. The information will be duplicated on each page within your website.

However, in an ideal world, each page should really have its own keywords and description.
Therefore, the default settings can be overwritten on individual pages by filling in the' Advanced Page Options' when adding or editing a page.

Editing the Advanced Page Options is completely optional but we highly recommend spending the time to fill in these areas. It will aid in Search Engine Optimisation.