The Two Column Layout offers left navigation and a fairly wide Main Content area. It is great for regular content and works well for displaying structured content, pictures, and data in tables, as well as web parts such as FAQ and Shared Site Content.
Here is an example of the Two Column Layout in edit mode:
Here's an example of how the Two Column Layout looks in site:
Changing the layout of a page is easy -- here's how:
Changing a Page Layout.