Does coffee taste different when it is ground at home? Is there a difference in the taste of the coffee that I grind myself versus the ground coffee that I buy from the store? Does the size of the ground change the taste of the coffee that I brew?
I bypass the first question.

Yes, ground size considerably affects the taste of the final cup. In general, there's a common rule of five component for a good cup of coffee. Each component must require its precedent.


Good beans
Good roasting
Homogenously/correct-sized grinding
Correct equipment
Skilled cook


(Italians mostly merge first two articles and name it as 4M for espresso.)

As stated above, the grounds must be all at the same size. Moreover they must be the correct size. The finest for Turkish, a bit less fine for espresso, boulders are good for French press, etc.