Elements/ Artist Channel Mapping

I’m new to this new-fangled electronic stuff, and was hoping one of you gurus could help!
I’m trying to connect a Casio CTK6200 via USB to Cubase Elements, and would like to map 16 channels from the Casio into Cubase - so that what plays on the Casio is captured as separate channels into Cubase. My ultimate goal is to insert/ edit chords into the sound track so they can be played back on the Casio along with the other tracks.

I can record one channel (the channel I am playing on the keyboard), but not the other 15 channels with backup/ rhythms.

If this possible, and if so could you kindly provide simple instructions/ reference a simple-minded person can comprehend?