Mean and Standard deviation for features as a whole and each of the classes? Help?

Using the attached .mat file I need to find the mean and standard deviation for the features as a whole and also for each of the classes, the code I currently have is:

>> mean(Xtr) + mean(Xte) %This is what I think is the mean for the features as a whole? Not too sure what exactly and feature is in this context though?

>> mean(ttr) %This is for one of the classes?

>> mean(tte) %This is for another class?

and for standard devation I simply used the std() command

My main thing is im not understanding what a feature or a class is in this context as I am new to matlab? Am I on the right track at all? Any code that is of better use than what I am currently using?