Head over to your documents by using the left-hand menu from the dashboard:

Select which documents you want to export by using the checkboxes:

Once you've selected the documents you want to export, click on the download icon from the tool-bar:

You can choose between a basic export (Title, content & word count) or a comprehensive download that exports data such as SEO info and meta-data:

A CSV of your documents will be downloaded - this can take a minute.