Meta descriptions are the short sentences that appear in search results under the title of your listing. Having a good title and meta description can both help push you up the results pages and also increase your chance of a click-through.
Your website auto-generates a title for your website based on the name of your restaurant and the current page in your website. Titles like this tend to work best for restaurants.
The default meta description is just a basic descriptive sentence. You may want to change this, especially on your home page. An ideal meta description will have the keyword set you've chosen for optimization somewhere in a solid description of your website and restaurant. You only have 128 characters of less to do this, so keep the description short and sweet.
Your meta descriptions should describe the page content. It is a way to tell search engines "this is what this page is about". On your home page, this can be a general description of your restaurant. On other pages, if you stray too far from page content, the meta description will be ignored, and they will just use a snippet from your page somewhere.
Search engines aren't the only ones that see your meta description. Customers will see this as they search for your restaurant on Google. A spammy looking keyword-stuffed meta description may push you up the results, but being at #1 isn't useful if no one bothers to click on your link. Be sure to make the description welcoming to potential customers.