When you ADD, things get bigger, longer or more.
Example
Jane has 12 pencils.
Bill has 15 pencils.
How many do they have in total?
Answer
Add together 12 and 15.
Start at 12 and count on 15 to get 27 pencils.
12... 13... 14... 15... 16... 17... 18... 19... 20... 21... 22... 23... 24... 25... 26... 27
When you SUBTRACT, things get smaller, shorter, fewer or less.
Example
Jane has 17 marbles and gives 5 to her brother Bill.
How many does she have left?
Answer
Subtract 5 from 17 (17 - 5).
Start at 17 and count back 5.
17... 16... 15... 14... 13... 12
She has 12 left.