I hope its correct forum, please move to correct place if its not.

I never tried to make Tetris in Turbo (Borland) Pascal/Delphi. And today i was thinking about starting writing one. Just to learn more. Is there any tutorial about creating Tetris in Pascal/Delphi? Just very basic, without score stuff etc. I just need some algo how this all must be done. I know that tetris game uses alot of arrays. I have some sources but almost all of them is without comments.
Can somebody give me some point/algorithm to start?
Im not beginner in programming, just some stuff is still new for me.
And what knowledge i must have?
Thanks in advance.