Elementary School Mathematics/Number Operations
There are four basic operations that are the foundations for every other kind of mathematics. They are addition, subtraction, multiplication, and division. There are other, more complex operations, but these are the four absolutely basic ones. They cannot be simplified, they cannot be reduced. They cannot even be proven without referencing themselves. They are the "assumptions" of all math - we assume that they are true because we know they are because we created them, not because we can mathematically prove it.
These four basic operations are collectively known as "arithmetic."
Addition is the process of adding one number to another. For every problem, we always start at 0. Try 1+2 = 3. Starting from 0, we move a distance of "1" on the number line. From there, we move a distance of "2" on the number line. When we look around to see where we are, we find that we are a distance of "3" from 0. Thus, the answer to our equation is 3.
Subtraction is the process of removing one number from another. Start from the number line position of the first number in the equation, then count backwards the amount of the second number. For 5-3, we start at the position of 5 on the number line, then count backwards 3, leaving us a distance of "2" from zero.