Hey there!
Let's think of both of these functions as two different slope-intercept equations (y=mx+b). Don't let all of the fs and gs confuse you; those are just showing that they are two different functions!
Our function f has an equation of y=x, which is a diagonal line that passes through the origin and goes across each small grid on the graph diagonally.
Our function g has an equation of y=-1/3x+2, which means that it will intersect with the y-axis at two units above the origin and for every three whole steps it goes to the right, it will have gradually gone down one whole step as well.
Attached to my answer is what a graph of it would kind of look like. Sorry if the lines don't look too much like a line it's a bit difficult to draw with a mouse haha!
I hope that this helps! Have a wonderful day!