If you don't understand WHY you are doing something, then you are left with learning the so called 'parrot' fashion. i.e. memorising.
Try word association:
You can remember stuff like expanding brackets by using acronyms such as FOIL (Fronts, Outsides, Insides, Lasts).
Pi (3.14159) can be remembered by using May I Have A Number Instantly i.e. use the number of letters in each word May = 3, I = 1, Have = 4, A = 1 etc.
Formula for the circumference of a circle might be C=Pi.D i.e. Circumference= Diameter x Pi or Cherry makes Delicious Pie's.
You can use this technique for other longer strings like the first twenty elements of the periodic table: Hydrogen, Helium, Lithium, Beryllium, Boron, Carbon etc........using something like: Horrid Henry Likes Beating Boring Children Not Only For Never........you get the idea.