It is very instructive to note that the framers of the Constitution chose the indefinite article ‘a’ to describe the Militia as opposed the definite article ‘the’. Additionally the second amendment absolutely does NOT say who or what would regulate the Militia.
So, where does that leave us?
Quite simply, the word ‘Regulated’ before Militia refers to a condition of readiness and preparation to fulfill it’s duty as a Militia. That, literally, is all it means and it’s no more complicated than that.
Those who cry loud and long that ‘Well Regulated’ refers to a condition of regulations applied by a central authority such as the government are either showing their ignorance of fact, or are lying. Quite honestly, the later condition is the norm.
It really IS that simple.
God bless you and yours.