You should enter a meta description for each one of your pages. Use simple but informative sentences. The search engines will check how relevant your description is to the actual content of your page so make sure that you describe only the current page and avoid adding irrelevant information in the description.
It is a good practice to categorize your posts in articles. Once you go to the Posts -> Categories page in your admin area, note the description field available for each category. WordPress will take what you enter in this field and insert it as meta description for the category.