Let any integer be represented by x.
Then, the consecutive integer (the number that follows) should be x+1.
The statement wants us to prove;
(x+1)²-x²=x+(x+1) <-- solve left hand side
x²+x+x+1²-x²
2x+1 (solution for left hand side)
Now solve for right hand side.
x+(x+1)= 2x+1
As noticed, the LHS=RHS (left hand side= right hand side), therefore, the difference of squared consecutive numbers subtracted is equal to the sum of the two integers.
Hope I helped :)