To know that a relation is a function is it the graph gets approved by the “vertical line text”. If the imaginary vertical lines you draw onto the graph only touch one part of the line, then it is a function. If they touch two or more parts of the line, then the relation isn’t a function.
(Since I cant see the following I’ll also give another tip) If the ordered pairs are given, then if a number in the x points is repeated, then it is not a function. But if I’m y is repeated, it doesn’t matter, it’s still a function. The only thing you need to focus on is on the x list, if one number is repeated then it is not a function.