What does the point (2120) represent on the graph?

As written (2120) does not mean a thing on a coordinate graph.

It is correctly written as ( 21,20) Note the comma.

(21,20) corresponds to ( x , y ) point on a coordinate graph.

On a coortdinate graph, from the origin (0,0) move '21' places to the right on the x-axis. On reaching there, go up '20' places , parallel to the y-axis.

Having gone up the '29' places, you are now at the point ( 21 ,20 ).

For a different coordinate points the figures could be ( 2,120) or ( 212,0)

Note the comma (,) is ALWAYS there.