Freedom is to be found in thinking, primarily (since action is constrained) - or, more exactly, from thinking of a certain type - but most thought is not free.
Thus, each man is born with potential for freedom - but will never or seldom actually be free unless or until he learns it, does it, and knows when he does it (learns the nature of freedom, learns to be free, and strives actually to be free - in awareness of doing so).
Freedom is divine - it is a property of divinity; and Men are free only because (and insofar as) they are gods.
What kind of gods are men? Two kinds of god (or god in two ways). We are 'children of God' - therefore first we are of embryonic god-nature (else we could not be children of God), and secondly we have God-within-us, parentally: by inheritance. To put it differently, we are generically-gods because we have God-in-us, and we are also uniquely-gods because we have something in us which is eternally existent and was not created.
I mean - we were eternally existent before our mortal lives, and before we became children of god - and it is this unique divinity in which our capacity for freedom is rooted. I nother words, God created us by shaping our pre-existent selves; but God did not create us utterly (or else; being entirely made by God, we would not and could not be free).
For us, as individual persons, to be free is to think actively from-our-selves (and not merely passively in response neither to stimuli, nor from God (either as divine input or divine programming).
So, a free thought comes from our unique and eternal divine self, and is not determined by anything else (although it may be influenced by many other things - but any influence is not the free thought's primary origin).
To make sense of the above - the self must be a 'given'; the self needs to be understood as something characteristic and unique in its nature which can give rise to thoughts from that nature, and from nothing else.
(Thus free thoughts are not merely random - randomness is not freedom. Free thoughts are thoughts which originate in our-selves.)
Even if most of our thoughts are not from that unique self, it must be possible for such thoughts to arise; and only such thoughts are free.
A person might live out their life and have no free thoughts - it is at least imaginable. Another person might have free thoughts - but never be aware of the fact.
But if one can imagine freedom in thinking, then one can potentially be free; and one can know that freedom when it occurs. And nothing is more sure than that knowledge.
(Now, you can answer the questions in the title.)