how we prepare a 4M solution of NaCl in 100ml and after this we dillute this 4ml solution to make3.8M solution.

Answer 1

How many mols NaCl do you want in the 100 mL? That's M x L = 4M x 0.1L = 0.4 mols.
How many grams is that? That's
mols = grams/molar mass. You know molar mass and mols, substitute and solve for grams. Place that amount NaCl in a 100 mL volumetric flask, add DI water, swirl until dissolved, add DI water to the mark of the flask, stopper and mix thoroughly.
Then the dilution. You made a typo; I assume that is a 4M solution not 4 mL. How much of this solution do you want? That is substituted for mL2.

mL1 x M1 = mL2 x M2
mL1 x 4M = mL2 x 3.8 M