To plop render, press esc (should normally take you to the render screen, if you haven't rendered anything it should be white) or click the wireframe cube on the right side (several icons below the spraycan)until you get to this screen. Now click and hold the left mouse button and a maquee will appear. Drag it around the area you wnat to render and 2 buttons and a triangle will appear next to the box. Click these to render just that area (the small button stops and continues the render just like the normal buttons). Be careful not to click the normal render buttons or the whole render will be restarted. This is useful in example you have finished a render (maybe it took a long time) and you notice something is out of place or you just want to make a minor change. Make your change, go back to the render and outline that small area just to render that part and save when finished.