Gravity is a weak force, Newton guessed (correctly) that that same force that made the apple fall from the tree kept the moon in orbit around the Earth

'Weightlessness'

The best way to think about this is that you are just falling inside an airplane that is also falling

So the net acceleration due to gravity is zero.

What about your mass? Has this changed?

So when you 'weigh 50kg' is this correct, scientifically speaking?

'Weight' is a Force, measured in newtons (N)

F=ma

So 'weight' on Earth is proportional to mass, and most scales use this proportionality to give your 'mass' instead of your 'weight'

If F=ma, what is the 'a' in this formula?

a is acceleration due to gravity, given the symbol g