Show all windows/preview windows

[Mark]

I hear that the Mac has a function whereby you can hover the mouse
over a minimized window icon and see a preview of what's in that
window (similar to hovering the mouse over a tab in Seamonkey - you
get a small preview of what's in that tab).

I've also somehow (accidentally) run into a feature whereby I get a
preview of every window in a workspace.  The only trouble I have with
this is that I've never done it on purpose, only when I trip some
combination of mouse and/or keystrokes that just makes it come up.

What and where are these commands and how can I invoke them on purpose?

Thanks.