Math operations must be done in the following order:

    1) Parentheses
    2) Exponents
    3) Multiplication
    4) Division
    5) Addition
    6) Subtraction

A good way to remember the order is using a mnumonic device.  In other words:

                           PLEASE                Parentheses
                          EXCUSE                Exponents
                           MY                       Multiplication
                           DEAR                    Divsion
                           AUNT                    Addition
                           SALLY                  Subtraction

Now it should be easy to remember the order of operations and when to do which one first!  Now, I'll show you an example!!
 
 

  Here is the following expression:                            (6 * (7 - 4) - 42 + 8) / 2

1) Do PARENTHESES, inner pair first.                  (6 * (7 - 4) - 42 + 8) / 2 = (6 * 3 - 42 + 8) / 2

2) Do EXPONENTS next.                                             (6 * 3 - 42 + 8) / 2 = (6 * 3 - 16 + 8) / 2

3) MULTIPLY next.                                                      (6 * 3 - 16 + 8) / 2 = (18 - 16 + 8) / 2

4) Divide next. The equation reads : (18 - 16 + 8) divide by 2.  Since the "2" is outside the parentheses, you must wait to divide.

5) Addition and then 6) Subtraction.  If all you have left is adding and subtracting within the parentheses, work left to right.  This is also true for multiplying and dividing.

                                                                                        (18 - 16 + 8) / 2 = (2 + 8) / 2
                                                                                                                   = 10 / 2
                                                                                                                   = 5

Way to go!!  Now that I've given you an example, I have a couple of practice problems you can work on to become better mathmeticians! Good luck!!