Hey there jerbearferrjerr,
Thanks for reaching out to Apple Support Communities. I understand you have some questions about using Deep Fusion. I’ll be happy to help.
Deep Fusion is an advanced image processing system, this means it is activated automatically. It uses the ‘A13 Bionic Neural Engine to capture multiple images at various exposures, run a pixel-by-pixel analysis, and fuse the highest quality parts of the images together resulting in photos with dramatically better texture, details, and reduced noise, especially for mid to low light scenes.’ This information can be found under iOS 13.2 > Camera from this site: About iOS 13 Updates. This is not a setting which you'll need to adjust.
For more info on taking photos with your iPhone, look at these articles:
Take great photos with iPhone
iPhone 11 and iPhone 11 Pro camera features
I hope that helps.