http://www.chemistry.usna.edu/plebechem/excel_tutor/homepage.html (US Naval Academy)
Thorough, step-by-step tutorial with many illustrations.
Part I: Creating a Spreadsheet, Entering Information, Formatting, Saving the Spreadsheet, Finding Your File, Closing and Opening a File, Making a Chart (a.k.a. Graph), Modifying a Graph, Printing
Part II: Block Copy, Inserting a Row and a Column, Formulas, Addresses, @ Functions
Part III:  Trendlines and Graphing

http://science.csustan.edu/tutorial/Excel/   (California State University, Stanislaus)
Thorough tutorial covers everything from getting started through linear regression.  Lots of text, few illustrations can make for dull reading, however

http://www.wellesley.edu/Chemistry/Flick/excel1.html  (Wellesley College)
A very brief tutorial that quickly shows you how to make a graph

http://www2.ncsu.edu/ncsu/chemistry/resource/excel/excel.html  (North Carolina State University)  graphing and trendlines

http://www.cba.nau.edu/allen-d/Excel Regression Tutorial/excel_regression_tutorial.htm
(Northern Arizona University)  tutorial on linear regression

http://www.science.richmond.edu/chem/faculty/stevenson/301/Excel_General.html  (University of Richmond)  graphing, trendlines, and linear regression