Um.
When you render it should automatically create an image file in your specified location, or it will ask you, or there will be a save button.
As for unrendered sketchup models, I'm sure there is some sort of a function to take pictures in Sketchup, but you can always print screen. (Hit the PrtSc/Print Screen button on your keyboard and go into a paint app and Ctrl + V [Paste] the image in, then save it)