First, let's give those two numbers some names. We'll call the first one A and the second one B.
The word "sum" in math always looks like +
The word "difference" in math always looks like -
So, if we want to write "The sum of two numbers is 14" we would write A + B = 14
And if we want to write "The difference of two numbers is 6" we would write A - B = 6
I hope this helps! :)