I'd start with reading the Matrix spec, you'll want to know how the syncing protocol works, and this will give you enough familiarity that you can start playing around with curl to actually see it in action. I'd highly recommend understanding how conflict resolution works, the "Analysis of the Matrix Event GraphReplicated Data Type"[0] lays it out pretty well.

Matrix-CRDT posted here should abstract most of the nitty gritty stuff, but there are no shortcuts to designing with CRDTs so familiarizing yourself with those is important.

Other than that, just start playing and asking questions! The #matrix:matrix.org room is full of friendly and helpful people and I'm sure you'd be able to get answers.

[0]https://arxiv.org/pdf/2011.06488.pdf