The term "printing" encompasses any number of different processes, purposes and an enormous variety of skills. What do you want to learn how to print? Paper, fabric, signs, billboards, beverage coasters, fine art prints, magazines, mouse pads, automotive sales financial disclosures, novelty piggy banks...
There is no way to learn "everything" about all printing and there's no easy way to learn "most stuff" about any one particular process.
If you are more specific about what your goals are, we can probably point you in some directions. Cheers!