This video goes over the various ways of expressing concentration including molarity, percent by mass, percent by volume, and percent mass over volume.
Molarity, in particular, is important in chemistry and allows one to quickly calculate moles of solute in reactant solutions. MxV = n
The "Dilution Formula" is also discussed for calculating the amount of additional solvent required to reach a target concentration when diluting a concentrated solution. M1V1 = M2V2
