Im an instrument tech by trade, PID tuning is one of our "things"
The below might help
Error - diference between what you want, and where you currently are
Proportional ("P" from PID) is the "gain" or multiplication factor, basically alters the control output by the Error multiplied by the gain
Integral or "Reset" ("I" from PID) Proportional will get you in the right direction, integral gets you to the finish line, after the "Proportional" bit has done its bit, integral slow sneaks the control values up to get to to where you want to be.
Derivitive ("D" from PID) is the bit that looks to the future..... it looks at the error, looks at how fast you are moving towards where you want to go, and starts backing things off to stop you from over shooting.
To much "P" or Gain , you will see oscillation
To much "I" you will see it fly well past set point "integral windup" as it over compensates, followed by undershooting, ad so on, looks like oscilations, but much slower.
To Much "D" you will see your multirotor attempt to correct, get part way, stop, and then go again, sort of two steps forward, one back. not enough D, you will get over shoot.
Always Adjust P first, then add I to get things back to set point, play with D last