First you should crop it to the ratio for the Print you want made (eg. 6x4, 8x10, etc)
Second you select the thumbnail and click on [Export]
Fill in the Export options,
And finally click on [Export] at the bottom of the export dialog window.
You will learn all the options in the Export dialog with time, but for now, do something like the screenclip below-
Export to a folder on the hard-drive- you can copy it to the thumb-drive later. Or you can select the USB thumb-drive if you click in the panel "Export Location">Set it to Specific Folder>[Choose]
Use settings in the screenclip (and the closed panels should be 'empty' or no option set)
After a successful export you could save this dialog with these settings as a Preset by clicking the [Add] button tat will be visible in the lower-left corner.
Thank you very much indeed