I sometimes get messed up by the three rendering methods:
Controller::render()Controller::renderPartial()Co
Render File:
Will run the rendering methods on a given file with the set rendering engine. This is fairly low level within Yii and only really used internally or in console commands.
Render Partial:
This takes the alias given and converts it into a file path using all the local variables such as current running controllers and modules and alias definitions. It then pretty much just uses render file.
Render:
This is combination of render partials to make our lives easier. It will render the layout on the currently active contoller, or the defined one, render all the content within it, handle caching of renders, and process the output for client scripts.
Hope that clears it up.