Just a clarification there: NOT is a logical (or boolean) operator (like AND, OR), not a relational operator (like <, >, =).
To check if a is not equal to b, you can do it two ways:
1: IF a <> b then...
2: IF NOT a = b then...
The NOT operator simply reverses the outcome of the same check done without it. Regardless of the values of a and be, one of the following two commands will always evaluate TRUE and the other one will always evaluate FALSE:
1: IF a = b then...
2: IF NOT a = b then...
You can use NOT with
any type of check you'd use IF for, not just for checking for 0's or 1's. You can use it in complex formula that are made less complex by reversing checks, or with string comparisons. It's especially useful in logical bitwise operations, though these are possibly in the upper tier of understanding.
In short, if you have an expression that evaluates to TRUE, putting a NOT in after the IF will make it evaluate to FALSE, and vice versa.