want to know how to derive dimensional formula

Let's take an example:

if we want to find the dimensional formula of force, then taking

F = m a

Now putting dimensions of m and a in the above expression

[F] = [M] [LT^-2] = [MLT^-2]

Therefore to derive the dimensional formula of any physical quantity, take first the relation of that quantity and put the dimensions of the quantities comming in the expression.