type "free tutorials *" where * is the program you want to learn.
you will most likely find quite a few interesting tutorials. you may even find enough to train yourself on the program.
however, you should not expect the level of detail and ease of use that you would get from buying a propper book on the subject. and as for mastering the software? that is completely up to you and practice.
suggestion: go buy a textbook for the cad you want to master. read through, practice, then sketch various drawings from scratch and model things in 3d from drawings. that is the ONLY way you will master the program.