The arrows on the left allow you to flip through pages without scrolling.
You can go directly to the page you left off by inserting the page number you want after the word 'Page.'
The - + symbols allow you to zoom in and out.
The final symbol on the right expands the page to full size.
You can scroll as well as flip through pages depending on your comfort level.
The mobile version is a normal sized pdf stripped of any web graphics to make the loading faster. It can be used for PC reading as well if you prefer scrolling to page flipping. I find the vertical layout cumbersome for reading on PC but others may not.