No problem Hayley, if you want to walk through it with me... I am very patient. My goal will be to help you to understand how functions work. Once you understand that, the rest is pretty straightfoward.
Let's start with the first function -
f(x) = -2x + 3
Think about this function as a machine. You put in one number and you get out another number. We will call the in number the "input" and we will call the out number the "result".
We can write this in math (like we did above) or we can write the same machine in words
For the function named 'f', you get the result by multiplying the input number by -2 and then adding three
You can try either one of these forms (they work the same)... and I will let you try.
If you put a number 1 as the input to the machine (function), what will the result be?
If you put a number 3 as the input to the function, what will the result be?
If you put a number 0 into the function, what will the result be? (I am rewording the question a bit but is the same question).
You can ask this type of question by simply saying f(2) = ? ... but it helps to think about what you are doing is putting some value into this function and getting a result.
Is this helpful so far?