Functions are a type of relations, so all functions are relations but not all relations are functions.
Relations can be any two number pairs, but functions are different.
For every input number, there is only one output. But one output number can have multiple inputs.
For example, if the coordinates are (1,4)(2,6) (3,4) that is a function, but if the coordinates are (3, 7) (6, 8) (3, 5) that is not a function since 3 has 2 different outputs.
Another way to check for functions is a vertical line test. This is used when you have a graph, you can imagine a vertical line going across the graph, and if it ever comes across 2 points at once, it is a relation and NOT A FUNCTION.
If the vertical line goes across the graph and never touches 2 points at once, then it is a function.