From your Dashboard, navigate to Design -> Pages. In the top right corner, click the Add button. You can also edit the pages by clicking on the "Edit" button.
From there you can fill out the title of the page and enter any content you'd like. Once you have saved the page, you will need to add it to a Navigation bar so that customers can find it. To do this, navigate to Design -> Navigation. Choose if you would like your page to appear in the top or bottom navigation bar, then click the appropriate Add button. You will then enter the name of the page as you'd like it to appear in the navigation bar. Then from the "Link to" dropdown menu select "Page". At this point, a second drop down menu will appear. Just select your new page and click 'add'.