Here is a video of Adam explaining the strategy of making 10 to add and subtract.
Note that when you are adding , he will make a number bond using the larger number and adding it to the smaller number to make the number ten. i.e.: 13 + 5, I would take 5 from 13 and add it to the other 5, making 10. Then use the rest of my 13 number bond, 8, and add it to my 10. 8+10= 18. Of course I could just count on, but learning this strategy will help with larger sums.
When subtracting, say 13 – 5, I will make a number bond with the larger number, but turn it into 10 and what’s left. So 13 becomes 10 and 3, then I will take the 10 and subtract the 5, 10 – 5 = 5. Now add the numbers 5 and 3, they are what is left after the subtraction and that is the answer. Hopefully you will see this in Adam’s explanation!