Hi!
Addition, subtraction, multiplication, and division are all just what we like to call the four essential operations of arithmetic.
These operators are the foundational basis of any mathematical expression or equation. We use these operators in our daily lives.
For example, look into a field of cows. You might count them, and say 'There are 10 cows in this field'. But then, suddenly, one you didn't see comes to view. You'd now say 'Oh, there are 11 cows!'. You just did addition.
You added 1, to 10. As a result, you got 11.
Another possibility would be looking out your window while on a car ride. You might be counting the number of same brands of cars you see.
Again, this will be addition. An example of subtraction would be realising you made a mistake and included a Ford car when you were looking for Chevies. You'd then take 1 away from your total, consequently resulting in subtraction.
Like I said, these operations are essential to the basis of all mathematical expressions. What I mean by that, is that they almost always will be included, and you will always use them in one way or another.
Take the expression 6x + 8 = 10 for example.
In order to solve for x, we'd have to do the operators we discussed. Perhaps not always all of them, but you never know!
Hopefully, this helps! =)