The Wolfram Language can be used to make plots of functions. You give the Wolfram Language a function, and it builds up a curve or surface by evaluating the function at many different points.
Here we describe how you can make plots from lists of data, instead of functions. ("Importing and Exporting Data" discusses how to read data from external files and programs.) The Wolfram Language commands for plotting lists of data are direct analogs of the ones for plotting functions.