I don’t really get this.

Answer:
The answer is H. II and III only.
Step-by-step explanation:
A simple way to tell if a relation is a function is by taking a look at the X value, which is on the left. If the X value repeats again (ex: (0,1) (0,2) or (5,3 (5,7)) it is not a function. However, the Y value is allowed to repeat.