What is the definition of mass percent in chemistry?

How does mass percent relate to the molar mass of an element and a compound?

What is the mass percent of hydrogen in water (H₂O)? (Atomic masses: H = 1 g/mol, O = 16 g/mol)

For the compound Na₂CO₃, calculate the mass percent of sodium. (Atomic masses: Na = 23 g/mol, C = 12 g/mol, O = 16 g/mol)

In a pharmaceutical tablet, the mass percent of active ingredient is 25%. If the tablet weighs 200 mg, how much of the active ingredient is present?