Unable to Revert Commit

[Rex Macey <rex@macey.us>]

"Unable to Revert Commit ... Resolve the conflicts in your working 
directory and commit them before trying the revert again".  Please help 
me understand how to resolve the conflicts.  Here's what happened (as 
best as I remember).
Created a windows folder "github_learn" (not under my \documents\github  
folder) ;
Created a file file1.r.
Dragged folder into Github for Windows.  Committed; I could see the file 
in my directory, Github for Windows, and on the server (github.com);
I modified the first file.  Checked that there were different versions 
and then committed it.;
I created a second file, file2.r Committed it.  All good.;
Then I tested whether I could retrieve the first version of file1.r 
(before modification).  In the History area of Github for Windows, I can 
see this version.  I click on that, and then I click on "Revert" which 
produces the error.

I am very new to Git and have read some of the documentation and this 
exercise is my attempt to test myself.  So far my grade is not good.  I 
appreciate any guidance including links to instructions.
Thank you.
Rex Macey