If you know the name and location of your input file, you can type this information into the File Name entry field at the top of the main window. 

Otherwise, click on the Browse button to open a standard Windows dialog box that allows you to select the input file of your choice. Your input file should have the extension “.in” and be in the form of a flat, ASCII text file.

Select the file and click Open. The file name and location will populate the File Name field.