I have found learning mastercam by going to nightschool at a local college is best. I did have to talk to head instructor over the phone explaining that I was a manual machinist looking to update my skills and did not feel the need for taking all the basic machining courses and did not need a machining certificate.
By having a live instructor he shows all the students how to use Mastercam.
He also is there to answer questions that beginners would have trouble finding quick answers in the help documentation. Also if you have a "how would you do this" question he can demonstrate it.
Buying Mastercam books from eMastercam online is 2nd best way to learn. The books although not cheap are cheaper than paying for nightschool. I bought the Mastercam handbooks, mill tutorial, lathe tutorial books.
Not all the books come with the mastercam demo program. the demo works but will not save programs. but you can draw, post gcode. Usually the nightschool instructor can get you a demo cd if you do not have one. I learned mill first then later the lathe. The lathe is harder as you have to learn the default safety tool clearances and how to override them like when turning a concave part. Or using different approach angles. Or making a new lathe tool, that is setting it up in mastercam a tool you might be holding in your hand. Somethings like transferring gcode by rs-232 serial cable or floppy disk you may have to learn by doing. Often an older machine changes the uploaded gcode and you have to download it back to a laptop to see what it changed. That is not so much a mastercam problem more a using and maybe adjusting a post precessor for a specific machine. Some machines have some defaults in the controller than sometimes can be hard to understand. Again sometimes a live instructor and or experienced CNC machinist can answer in a few minutes and show how to do something that may cause a student to be stuck trying to figure out a solution for a long time.
Sometimes going to nightschool forces you to finish the course in a reasonable time. Other methods sometime people get bored and do not finish.
This is just my opinion.