Molarity is obtained by dividing the number of moles by the volume of the solution in liters. Therefore, the number of moles is the product of molarity and volume.
n = (100 mL) x (1 L / 1000 mL) x (0.10 M) = 0.01 moles
Multiply this value with the molar mass of NaCl to obtain the amount of substance in mass,
m = (0.01 moles) x (58.45 g/ mol) = 0.5845 g