chemistry help!!?

Enthalpy of combustion is the enthalpy change for a reaction, normally of an organic compound (contains C, H O, N...) with O2 to form CO2, H2O and sometimes a couple other things.

So, the enthalpy of combustion of ethanol (C2H5OH) would be Delta H for the reaction:
C2H5OH(l) + 3 O2(g) --> 2 CO2(g) + 3 H2O(l)

The enthalpy of formation is defined as Delta H for the reaction that forms 1 mole of a compound from its elements in their standard states. So, the enthalpy of formation of ethanol would be Delta H for the reaction:
2C(graphite) + 3 H2(g) + 1/2 O2(g) --> C2H5OH(l)

To the bottom like is that each of the specific types of enthalpies are for specific types of reactions.

As far as your second question goes, Delta H values usually have units of kJ/mol, and the mole properly refers to "moles of the reaction". In a simple reaction like HCl and NaOH, the balanced equation is:
HCl(aq) + NaOH(aq) --> NaCl(aq) + H2O(l)
Because everything is in a 1:1 mol ratio, you should actually use moles of NaCl formed. This would be equal to moles of your limiting reactant. Now, if you use the same number of moles of HCl as you do of NaOH, then it is a wash, and it doesn't matter which you use in the calculation. But if you have an excess of HCl over NaOH, then you would use moles of NaOH (the limiting reactant) because that is the same as moles of NaCl that you can form.

Does that help at all?