How do you get glasses from a source other than your eye doctor's office? do you just bring the prescription?

Yes: You can have the eye doc who did exam write out your prescription, which you can take elsewhere for glasses. If you have pair of glasses with current prescription lenses, an eye glass vender can read the prescription from the lenses & make a new pair with frames of your choice. Or you can have eye exam at chain eye glasses places & choose frames & lenses from their selection.