Hello and welcome to the forum,
What in particular are you interested in? Do you intend to become a programmer or work in some other area?
You might look here for the Hercules pc-loadable mainframe emulator:
http://www.hercules-390.org/Hercules will you to run "mainframe things" on your pc, but it typically requires a rather thorough understanding of the IBM mainframe environment.
Depending on your interest, i'd suggest looking for an education center near your location and enroll there for some training.
Keep in mind that systems like Linux, and Windows are meant to be "run out of the box" (i.e. anyone can install and run them). This is not the case with the mainframe. . .