Note: that this isn’t finished and hasn’t been updated since 2003 might be a turn-off at a glance, but don’t let this detract you. Almost all information in it is still relevant today for zsh (or indeed, Bourne shells in general) and I found it very well-written. When I switched from tcsh to zsh a few years ago I found it a great read that I learned a lot from.
I’d almost forget about sourceforge.net by this point, I’m surprise it’s still alive.
This guide is how I taught my high-school self shell and a lot of Unix in general back in the late 90ied. It’s extremely well written and serves as an excellent intro into (Bourne-) shells and of course it highlights all the great things zsh has over the competition.
This guide also meant that zsh was the shell I’m most familiar with and thus it’s my default shell on all the machines where I have the liberty of choosing a shell