Not a particularly complete answer ... ...
though from what you've stated it's not a particularly capable machine. These programs are resource/hardware intensive.
To "render" a timeline, you select a section, right-click, and from the options that pop up choose "render" that section. It means that PrPro will create a "preview" for that area to use in playback, though any time you change anything on that bit you'll need to render it again.
NOT the same as render-out meaning to export out for other use.
Neil