Lab documents are structured hierarchically. At the top of the hierarchy is the Contents page. The entries on this page are called chapters, and any one of them can be accessed by clicking on its title.
Chapters can be further subdivided into sections, which may then be divided into subsections, etc. The table of contents in the frame to the left helps you through this hierarchy. The contents entry displayed in white tells you your current location within the lab. To access any of the other chapters or sections, simply click on the appropriate entry.
Other chapters in this lab are titled "Simple Calculations", "Simulations" and "Using simulation to estimate the value of PI". You will note that long titles for chapters don't show up in their entirety in the table of contents frame. I'll try to avoid them! You can get to any section of any chapter by clicking in the table of contents frame. If you want to go on directly to one of the exercises, read the section on Lab Reports and then move to Simple Calculations.
One warning. If you don't click on a section's link in the table of contents, you may skip right by it. For example, you will not see the subsection "Emacs Electric C mode" of the next section unless you click for it.