At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus.
Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
You can think of a function sort of like a box where you put something in and it comes out the other side different but with a consistent pattern. So, in this case, 1 goes in and comes out 1; 2 goes in and comes out 4; 3 goes in and comes out 9; 4 goes in and comes out 16; 5 goes in and comes out 25. We know that there is definitely a pattern, because we are told it is a function, but what is the pattern?
So, first we can look at addition. 1 goes in, we add 0 to it to get 1. 2 goes in, if we add 0 to 2, we get 2, which is incorrect.
So, now we look at multiplication/division. 1 goes in, we multiply by 1 and get 1. 2 goes in, we multiply it by 1, and get 2... so nope, no answer there either.
So, now what else is there to look for? Usually next in these easier patterns you will look at exponential. So, 1 goes in, 1 to the power of anything is 1. Now lets look at the 2nd one. 2 to what power is 4? 2 to the power of 2 is 4. Let's check the next one. 3 to the power of 2 is 9... so the pattern seems to work. If we test every entry, we will find that the pattern is that whatever goes in is square to get the result.
Make sense? The more algebra you do, the better grasp you will get and the faster you will become. Good luck! =)