If the representation is a graph then use the vertical line test. Draw or imagine straight vertical lines going down the graph. If the vertical line only goes through the function line one time then it is a function. For an example, a circle on a coordinate plane is not a function but a wavy line is. If the representation is a table with points then look at the x values. If x repeats then it is not a function.
The dividend on top (the number that's being divided) then / and the divisor on the bottom (numbers that's dividing the other). Example 20 divided by 5. Would be 20/5. Ask anytime;)
