Formating

Which version are you talking of?

When you mean what I think you mean - thats easily to achieve in Mathcad 15 (and below) but is one of the many missing features in Prime.

Mathcad 15:

In Prime the "show indices" button in the "Result format" section on the "Matrices/Tables" ribbon will only work, if the matrix is so large that it is not fully displayed.

Afterthought - if you are talking about labels you apply yourself, not row and column indices, then the only way is to add them is as strings (which does not look that good). If you are using Prime and are talking about a matrix with values you manually type in, you may also consider using a "table". But its use is very limited (only column labels)  and it can not be used for displaying a matrix, only for input/assignment.

But maybe you simply are too much used to think in columns and rows because you have used a spreadsheet program for too long ;-). Simply assign the columns or rows of interest to variables with meaningful names and use those variables in your calculations.

Any specific example you are interested in?