After creating a page group, you can add content to it. First you will need to add sections to your page. In the sections you will add widgets which display different type of information.
When editing the page you can always add more sections from the bottom of the page, under "Add section". Choose the preferred layout of the widgets for your section. You can see all the layouts by clicking Show all.
You can change the layout and style of the section after adding it. There are more layout types to choose from and from section styles you can for example add padding or a background image for the section.
Always remember to save from the bottom of the panel!
After creating a section, you will need to add widgets to it. There are loads of different widgets you can add. Add widgets by clicking the Add widget inside a section.