A one molarity salt solution is made by adding one mole of salt to a beaker and adding water until one has one liter of solution. A one molality solt solution is made by adding one mole of salt to a beaker and adding one liter of water. The concentration of the solution is an indication of the amount of solute present relative to the amount of solvent. Mole fraction is the ratio of the number of moles of substance relative to the total number of moles in the solution. Molarity is the number of moles of solute per liter of solution.
Molality is the number of moles of solute per liter of solvent.