The associative property of addition is the way in which 3 or more numbers are grouped for addition.  The order does not change their sum.  You should remember to do the adding that you see in ( ) first.

Let's see how that looks.  With pictures it would not matter which sets we combined first, in the end the sum of all sets would be the same.

( +)+ = + (+)              6+3=9                                                                        3+0=3

                           9+0=9                           6+3=9       

                                                  9 = 9

  +( +) = ( + ) +

          3 + 2= 5                               5 + 3 = 8

          5  +  5 = 10                                                       8  +  2  =10

                                         10  =  10