The in-built PDF viewer allows you to see your LaTeX document and the output PDF side by side. With auto-typeset on (see the section on Typesetting), the PDF is updated live to reflect the changes you make to the source code.
The small toolbar at the bottom of the PDF provides convenient standard functions to alter the appearance of the displayed PDF. The Editor-PDF scroll lock allows you to navigate the document with the input (the LaTeX source code) and the output (the PDF) scrolling in sync with each other.
You can also zoom in and out, set a particular zoom level and send the PDF to an external display.