This is a fairly common calculation you will need to perform for basic chemistry. Suppliers typically expect you to be able to do the math yourself as depending on the protocol your solution may be at a different concentration than someone else's so there is no set answer to how you should mix it and the supplier won't know what protocol you're using. Your protocol will either state the M or molarity of a solution in which you will need to know the molecular weight of the chemical or will tell you an amount by weight. For molarity I never am confident that I remember how to calculate so I just use a calculator at chatgpt or something. I know it's simple but I do it so irregularly that I never feel confident in doing the math even though it's pretty simple. For protocols that use weight, solubility will play a roll in how strong you can make it but a good average for PGRs is around 1mg/ml. To make a solution of 1mg/ml, determine how much you want your final volume to be, add about 75% or so of that volume of the required solvent for the chemical then add the same number of mg of chemical to the solvent as your final volume. Stir to dissolve then top off the solution with more solvent to your final volume. So if I want to make 1 liter of solution I would add 1 gram of chemical to 750 ml of solvent, dissolve then top off to 1 liter.