Tooling U is a great option to get a start. They let you keep the files via PDF format which you can save to your flash drive and print out later into a binder. I turned mine into binders so i would have a paper copy for quick viewing. I would also check out Sandvik/Coromants online course as well. If yo complete it within 6 months the course is free and they send you a text book. All that is online is the tests. If just getting started, after you have done the book work to get an understanding of machining I would find someone that will let you use some manual machines to get a feel for what it is to be a machinist. With being a Machinist comes some book knowledge and some practical hands on. Be sure to buy good micrometers and calipers. I would suggest Browne and Sharpe.Also learn to use vernier style micrometers and dial calipers before doing the Digital kind.There is nothing more aggravating than seeing someone that doesn't know how to read vernier graduated tools. I would also suggest getting a Machinerys handbook as well, to most of us in the metal working world it is like our version of the Bible. Get the print version. Good Luck! Let me know if you have anymore questions.
