NAD+ accepts two hydrogen from different kinds of molecules.
Polyatomic ion with a +1 charge
Takes 2 H from another molecule
One of the Hs bonds to NAD+ making NADH and the other H just kind of floats off as a proton, leaving its electron attached to NADH.
NAD+ works with oxidation reactions ( removal of two hydrogen ) like dehydrogenation.
NAD+ also helps in oxidation of aldehydes.
NAD+ takes the two Hs off of H2O, leaving the O which places itself between the C-H in the Aldehyde, thus oxidizing it and creating a carboxylic acid.
So, NAD+ can take two hydrogens from different kinds of molecules.