What is the dilution formula? I have not learned this,

Answer 1

c1v1 = c2v2
c = concn
v = volume

For example.
You have 2M NaOH and you want to make 500 mL of 0.25M. How much of the 2M stuff do you take?
2M*x mL = 0.25M*500 mL
mL = (0.25*500/2) = 62.5 mL

So you take 62.5 mL of 2M NaOH, add to 500 mL volumetric flask and make to the mark. This will give you 500 mL of 0.25M NaOH.