Q: where do I start with learning how to make keyboard accompaniment parts?
A: learn the melody for "twinkle twinkle little star" (or the alphabet song), in the key of C, and then learn how to play chords C, F, and G. then see if you can figure out which ones to play along to each moment of the melody. the whole song can be done very nicely in this way. see if you can put it together. the 3 chords spelled out are: C major chord is these notes: middle C, then E above that, then G above that. F major chord is these notes: middle C then F above that then A above that. G major chord is these notes: D right above middle C, then G above that, then B above that. You could switch these notes in any order but I've given them to you all staying in a reasonable range. so sing the song through in the key of C (starting on the note C for the first note of the song) and then see which chords of those 3 chords you think feel the best at which parts. see which ones seem to make the song sound the most strongly like itself. should be easy and fun, at least it was for me