The Save dialog allows for several options in how you save your grid.
Directory: Use the directory controls to determine where on your hard drive to save your grid file.
File name: Choose a file name. As for file extensions (the 3 characters often used after a period in file names), the application will automatically attach GEODAS standard file extensions to the end of your file name, if you haven't entered an extension yourself. You are encouraged to let the program add the file extension; this will identify the type of grid, making it easier for Grid Translator and other GEODAS applications to find your grid files.
Save as type: This will be set to save the file according to the format you chose in the Grid Options Dialog.