Is there anything particularly different about mainframes compared to working on a server besides it probably being a different operating system? I assume it has a command line and you ssh into it somehow (or something similar)? Or are they still running punch cards or something?
You can find videos on Youtube, it's like an IDE where you would do everything in a user interface with menus, but the interface is a 25x80-char screen only :-) Everything is "almost" similar to a Unix system, but with different names, files are called "datasets", there are very few tools, but every one of them has a language to do very complex tasks...
It's a very different (and foreign) environment. Job control language, how data is stored... if you come from a typical modern server environment you'd be pretty lost in the mainframe world.