AS400 BASICS ….anyone? I need advice

I am currently searching for basic knowledge/definition of AS400 platform basics. I have found very little specific knowledge for beginners. I have worked with this platform but only on a ‘one step removed’ basis, as I was a Sr. Analyst but not an IT person. Now, I thirst for this knowledge and have a great desire to learn more about it. Searches seem to result in every topic besides AS400 related stuff. I am not to proud to beg and need some direction here.