I finally figured this out just now after struggling for 2 days, and it was tricky for me to find the answers online so I thought I'd just make this post and answer it myself so that any other noobs struggling with this same problem might hopefully stumble across this.
My problem was:
- I had a rigged character from Mixamo
- I had several hairpiece meshes (top of head, back of head, mustache, beard, etc.) from which I had created hair using the particle system, separate from character mesh
- I wanted to have the hair sit on my character's head / face, and follow along with the rig
Tried joining it to character mesh, that didn't work Tried parenting it to rig, that didn't work Tried converting the particles to mesh and trying these other options again, that didn't work Tried other things I can't remember, and something always f-d up
In the end the solution was super simple, answer below: