The "Meta Description" is part of the HTML family of programming tags that help with your SEO efforts. Knowing how to program it and where it belongs inside each individual web page is not as important as knowing that you must have one for every page.
IMPORTANT: Cancel your service and find something different if your CMS does not give you the ability to change your Meta Description tag on every page of your website. Seriously. No Joke. No Control? CANCEL NOW!
The Meta Description is a 150 character or less description of what the visitor will find on your web page. The description needs to include as much detail as possible within 150 characters.
Assuming each page of your website is dedicated to a single Keyword Phrase as I previously explained, it should be easy to compose a terse 150 character description of each page.
Google uses the Meta Description on the search results page. It is the first thing a potential visitor sees before clicking into your website.
Your description is actually an online advertisement and you need to keep that in mind when composing it. Use up all 150 characters if possible, keep it interesting.
Don't simply use
"Our collection of 14k Gold Rings"
"14k Gold Rings, and other gold ring designs that are sure to put a smile on her face, and yours. Call us at 888-872-0274 to make an appointment."
That's 144 characters including spacing and punctuation. I feel that proper Meta Description writing is an art form and requires a little training to understand properly.