OK, when you're ready to do your final render you'll be best off using your own render settings. If you're not comfortable with this yet then just go with 'Final' until you get used to what's what.

Here's a pic to show you where to go in your render settings. Don't take much notice of my high AA settings, you'll more than likely not need this. For tests keep the subrays per pixel down to a respectable degree as render times rocket with these settings higher. If you think your image needs a bit more AA then adjust the slider accordingly.

Regarding AO. If you choose an atmosphere that already uses AO then it will automatically be selected. To change the AO settings or to choose it from a different atmosphere just go into the atmosphere editor under the Atmosphere tab at the top of the screen.