F-Stop, shutter speed, and iso are the biggest numbers to deal with.
1/60, sorta synced with stream/recording fps
1.4, lowest possible provided by your lens+body combination. Produces more bokeh in the background and lets more light in the lower this number is.
Too high and your image will have noise. Almost literally a brightness knob where high numbers are very bright and low numbers are not.
The core idea here is that you can separate out similarly colored objects (like your black shirt on a dark background) using light. You should have a light in front of you aimed at your face at minimum.