To add new content to any page, simply drag the widgy from the toolbar, as an example take heading widgy and place it on the page.
The blue line shows where the widgy will be placed. Heading editor pops up and now you can inserts any text you would like to.
Likewise, you may add: Headings, Text, Dividers, Images, Videos, Maps, Forms, Newsletters, HTML code for other Apps, by clicking on it.
All the changes that you've made will not be visible for your website visitors, until you click on the “Publish button”.