Here is a video to help you with concentration calculations. In Chemistry, concentration is know as molarity (i.e. the amount per volume).
Note that in the video, the lovely Tyler de Witt uses the unit “liter” for volume, but the correct international unit (as used by UK exam boards) is decimeters cubed (dm3) which is the same thing as Tyler’s “liter”.
This video does not quite use the right language for the various fractions as appropriate to the Edexcel iGCSE, but it is nevertheless a good description of the process. Make sure you use the notes on tutorMyself.com to get the exact language you will need for your exam.
And another somewhat older video showing the industrial process of fractional distillation: