The site layout is where you decide where content will be displayed for certain pages or all your pages. Widgets are used to display certain types of content. To access and edit your Layout, click on the Admin Bar > Appearance > Layout.
Here you can edit (by click on the gear icon), delete (clicking on the X), or move (drag and drop) widget to the sections you want them to appear in your site. You can also drag new widgets into sections like a sidebar to add different functions to your site (like a Twitter feed).
At the top of Layout there is a drop down menu called Site Section. Here you can decide which page layout you are editing. The Front Page is the default when you enter Layout. To save changes, click the Save button.