Calculating the absolute salt concentration of your stock solution will depend on your starting materials. Are you starting with a stock solution that is already made? If so, the concentration of the solution should be indicated on the bottle. If you are starting with the salt in solid form and will be making your stock solution yourself, you can determine the concentration by the amounts that you mix. If you tell me a little more about your starting materials, I can help you with your specific calculations.
In the mean time, here is a website that helps you understand calculations associated with concentrations:http://chemistry.about.com/od/lectureno ... ration.htm
Once you have a stock solution of known concentration and volume, it is fairly easy to determine the volume you need to make a dilution. There is a simple equation that only works for dilutions:
M1*V1 = M2*V2
M1 is the concentration in molarity (moles of solute / Liters of solution) of your starting solution.
V1 is the volume of your starting solution.
M2 is the concentration in molarity of your diluted solution.
V2 is the volume of your diluted solution.
To determine how much to dilute a solution to get a particular volume, let's do a simple example.
If I have a 1M solution of sodium chloride (NaCl), this means I have 1 mole of NaCl per liter of solution. Let's say I start with a liter of this solution, and I want to know how much water I need to add to make it a 0.5M solution.
M1*V1 = M2*V2
(1M)*(1L) = (0.5M)*V2
V2 = (1M)*(1L)/(0.5M) = 2L
So I need to add 1L of water, which will give me a total of 2L of solution. That will dilute my stock solution to 0.5M.
I hope this helps you get started. Please let me know what kind of solutions you are working with, and I will try to help you with the specific calculations.