Keep two discs synchronised?

I have run Hazel for years but only in its default mode, cleaning up deinstalls. I only recently learnt that it could do more but I'm pretty useless with scripts, rules, etc. Is there a simple way to get Hazel to keep the contents of two discs synchronised? Files/folders added/deleted on one are added/deleted on the other?

Hazel can only do a one way sync (i.e. mirror). If you want two way sync, I suggest getting a dedicated program for that. It helps to have something more interactive so you can handle conflicts.

That would help. Can you give me a hint as to how to set this up?

Check out this thread on using the Sync action: viewtopic.php?f=4&t=1593#p6500

I would very much recommend against trying this to do a two-way sync. Again, for that type of application, I suggest dedicated software.