Navigation buttons: Use the Left, Right and "Show All" buttons to change the context of what is being shown. For example, where a single page is selected, the left and right buttons will change the selection to the previous and next page (respectively) in the transaction.
By default, the transaction will show each page visited starting with the start step and ending with the end step, as defined in the transaction script. If a single page is selected, that page's DOM and page load times will be shown as normal using the red and blue vertical bars transiting the waterfall. If the content being shown has multiple pages, the DOM and page load times will not be shown.