How is the concentration of a solution measured?
C is the concentration
n is the number of moles and
V is the volume of solution
So firstly you need to know what is in the solution, I'll take HCl as an example:
Say you have 5g of HCl in a 500ml solution. You must first find the number of moles which is the mass in grams divide by the molar mass of HCl which would be 36.45g/mole. (1g/mole is Hydrogen and 35.45g/mole is Cl)
You get that answer then you divide by your volume in litres, which is 0.5L.
Your answer's unit will mol/L which is sometimes also known as just M.
Should get an answer of 0.27 mol/L for this example :)
Hope I helped :)