Settings set both in slicer and firmware and where to find documentation to go along with marlin's gcode/mcode reference list

When I have something set in firmware and the slicer also has settings for the same feature which are used? Specifically atm I'm wondering about firmware retraction and slicer retraction, will having both set cause a double retraction? What about with something like feedrate and acceleration would the slicer settings be used or the firmware settings?

I'm trying to dial in my printer's firmware, an ender 3 with btt skr mini e3 v2.0 + tft35 e3 v3. I finally did a print that wasn't just a test cube, I upped my retraction speed from 0.25mm@35mm/s to 0.25mm@40mm/s while I left my unretract settings as I normally have them at 0.25mm@40mm/s. I was having issues with getting gaps in my extrusion after a retraction or significant change in speed

Lowering my acceleration seems like it helped with the gaps, but I'm not sure how much bc I'm not sure which acceleration settings were used, prusaslicer's, or the firmwares. Same for my retraction, I'm not sure if my speed change was the reason for my terrible stringing, or bc I had completely disabled firmware retraction.

If someone could point me in the direction of some documentation it'd be greatly appreciated. I still don't understand how people get the values they use for their firmware or where I get info about the terms marlin uses when describing features in its listing of gcode/mcode. As an example G4/dwell https://marlinfw.org/docs/gcode/G004.html so I have an idea of what the planner is but I'm not sure where to find more info about it, the same goes for many other options in marlin, they use terms that I have no idea where to find official documentation/km) for the terms used