Addition of the matrix consists of adding the appropriate elements of the two matrices. You can only add matrices having the same dimension. The result of addition is a matrix of the same dimension. 

Similarly, the difference matrix is a matrix formed by subtracting the corresponding elements of two matrices of the same dimension. As a result, we obtain a matrix of the same dimension.

In annex I added examples.
In matrix there are two simple rules for addition and subtraction.

1.In each case the order of both the given matrices must be same.
2.Each element of first matrix shall be added to or subtracted from the corresponding  element of the 2nd matrix.