It's simple for a computer. For a spreadsheet, you can say IF (cellX) = (valueY) then {actionA} else {actionB}
In that instance, if the value in the cell is Y, the computer will perform {actionA}. If there is any other value other than Y, the statement is false and the computer will perform {actionB}
I use such formulas all the time. It's the easiest way to automate portions of spreadsheets. One is for 401(a) matching ... If the employee contribution is <= 3%, then the employer matches the employee contribution. Otherwise (if the employee contribution is greater than 3%), the employer contributes 3%.
Not necessarily. "If's" are like a fork in the road. The paths are neither true or untrue. They are simply paths. Suppose I choose path A and it led me over a cliff. My choice didn't cause path A to be the wrong choice. Whether or not I took path A, it would still have led over a cliff.
Example -
If 2+3=5, then...
A - 2+2=5 B - 3+2=5
No matter which answer I choose, answer A will always be wrong and answer B will always be right. My choice, whether right or wrong, has no bearing on that.