basically a gain acts like a capacitor,with a capacitor there has to be a certain amount of current passing through it for the led to light up (hypothetical),with a gain on an lm386,it means that that the current/volume being inputted must reach a certain level before it is outputted and amplified
imagine 50 people,50 being the smallest in height,and 1 being the tallest.
imagine them climbing over a small ledge (hypothetically),most will be able to get over it
make the ledge taller and less will get over
and so on and so fourth
instead of gain I prefer to call it "step" because it's more accurate