Question regarding moles:

So I'm having a hard time understanding the relationship betweenmoles, molar mass, atomic/molecular mass, and unified atomic massunits.

Is molar mass and atomic/molecular mass the same thing? It seemslike atomic/molecular mass is the sum of all the atomic masses in asubstance. The units for atomic/molecular mass is unified atomicunits and the units for molar mass is g/moles, so it seems likesome type of conversion is happening. A Helium atom has an atomicmass of 4.00 u and a molar mass of 4.00 g/mol. So is 1 u = 1 g/mol?Doesn't that go against the idea that 1 u = 1.66 * 10^-27 kg? I cansee that 1g/ mol = 10^-3 kg/mol, but how do you get rid of the molpart? Is it using the notion that in 1mole of gas there are 6.022 *10^23 molecules to get that conversion because 1.66 * 10^-27 kgneeds to equal 1 g/mol if 1g/mol = 1u?

Also physically, what is the difference between the mass of thesubstance and the atomic/molecular mass? If the substance is justthe mass of everything it contains wouldn't that be the same thingas adding up all the molecules making that substance? I'm alsoassuming that the atomic/molecular mass is the actual mass of theatom or molecule itself, is that the case? Or is it like the massof the nucleus of each atom (molecular mass would then be the sumof all the masses of all the nuclei). In that case, then the atomicmass doesnt include the mass of the electrons thus creating adifference between the actual mass of the substance and theatomic/molecular mass.