To navigate to Sections go to Sections > Sections. You can start by creating a new Section or by editing the existing one.
In either case you will see layout of the section. The section consists of individual widget boxes which can be filled with widgets. Each widget can be set up with a variety of content types and layouts. Each widget box has its own number and action menu.
In order to create a new widget please select the type of widget you need from the menu on the left side of the page, then drag and drop it to an empty widget box. Once you've positioned your widget, settings menu will open.
The most commonly used type of widget is Content widget. You can learn more about how to set it up here.