All theory-links (and most questions and answers of this SE) are giving information and exercises that you can train on any instrument, especially on keyboards. Look up fundamental theory.

I'll post you the very first best link I'll find when looking for music fundamentals

http://courses.missouristate.edu/MikeMurray/FundPrimer/PDFs/FundPrimerComplete.pdf

All theory-links (and most questions and answers of this SE) are giving information and exercises that you can train on any instrument, especially on keyboards. Look up fundamental theory.

I'll post you the very first best link I'll find when looking for music fundamentals

http://courses.missouristate.edu/MikeMurray/FundPrimer/PDFs/FundPrimerComplete.pdf

Update
This link is no longer valid, but the original can be found here:
http://web.archive.org/web/20201111204310/http://courses.missouristate.edu/MikeMurray/FundPrimer/PDFs/FundPrimerComplete.pdf