I used a combination of the help documents and CSSM. The help documents could guide me through specific syntaxes, but CSSM was valuable for learning what was most appropriate in what situation.
CSSM was also very valuable for learning about routines that I would have been unlikely to discover in my work. That was partly learning new ways to think about problems, and partly learning about routines and toolboxes that I do not need in my work but which I could assist others with.
The syntax of MATLAB is not difficult (though there are some tricks), but MATLAB overall has a very large library of routines, far too large for most people to keep track of. That is a strength, but also a problem.