Functions Will have names (it mostly matters when you have more than one) and typically people will use F, but it can be any letter.
The relation will tell us what to do when we have certain values
So if we have the function name and a 4 instead of and x, we will replace all the x values with 4. and at that point we would be able to find what the Y value would be if the x value was 4.
You can also get something where they tell you the Y value and you need to find the x value. To do this you’ll need to reverse the steps from the first example. So here we will subtract 21 by 7, then divide it by 2 and then there is our answer.