well ill define the mole for u.maybe that will help u.1 mole of any substance is that amount of that substance which contains 6*10^23 units of that substance..like if u have 1 mole of pages it contains those many no. of pages.1 mole of sweets=6*10...sweets.so 1 mole of molecules is like a collection of 6*10...molecules..and when i say amount it can be anything-like it may be amount in litres(volume)or amount in grams(weight).hope thats it..and remember in a chemical reaction its the moles that participate and not atoms.like 1 mole of N2 reacts with 3 Moles of H2 to produce 2 MOLES of NH3.and 1 mole of any substance weighs=its molecular/atomic weight(compound/atom) and occupies 22.4 litres at NTP.so u get the formulas quite naturally.u neednt mug them up. like if u have w grams of a substance
then
1 mol=Molevular weight(=M say)
ie When wt. is M mol=1
thus by unitary method
when weight is w mol=w/M.