If you are at a training institute then ask these questions of your teacher. If you are not, then enrol in one and ask your questions - if they are not answered by in the course of the teaching. Or type your questions into google and folow the links - especially the ones to IBM documentation. Wikipedia will give broad answers thar are reasonably, but not always, accurate. Or, just rock up to a company and say that you are interested in a mainframe career, have no knowledge but are willing to learn, and do they have any vacancies?
The problem I have is that people can explain things quickly but I can only comprehend slowly.