The directory to save the shot in must exist already: Screen-Shooter will not create it for you. If you try to save it to somewhere that does not exist, then nothing will happen. The default directory is ~/: your home directory.
Screen-Shooter is designed to allow the user maximum flexibility in naming each shot. The filename field (as well as the directory field) is passed to a shell for normal shell expansion before being used. This allows you to use the output of programs, scripts or environment variables to name your shots. The reason for this is to allow unique filenames, if the user desires. By default, Screen-Shooter will create a name which is based on the time and date it was taken. This should always be unique. The default filename is `date +%Y_%m_%d_%H%M%S`_shot.jpg. As you can see, the filename includes the output of the date command, in order to generate a datestamp. So it makes up a name based on the date, using the format the percentage symbols and letters tell it. Then it adds the rest of the name from outside the backticks to the date it has used. Explanations of the cryptic percentage symbols can be found in man date, but the arguments in the default filename are:
The hour of the day (from 00 to 23)
The minute of the hour (from 00 to 59)
The second of the minute (from 00 to 60)
The day of the month (from 01 to 31)
The month of the year (from 01 to 12)
The final two digits of the year
Other examples of filenames you might use are:
screenshot-`date +%Y%m%d-%H%M%S`.jpg
pic-`date +%H%M%S`.png
myshot.jpg
`my_own_script_to_create_a_filename`.jpg
The filename suffix determines the filetype. Screen-Shooter supports what can only be described as a ridiculous number of different image formats. Try your luck. For a full list, type man convert. You can even try .html to create a client-side image map, and wild things like that.
If your filename suffix is not something Screen-Shooter recognises, or you omit one, it will save the shot as a MIFF file. Use the convert utility to change the format later.
This checkbox is unchecked by default. After checking it, you will get a view of the shot once it has been taken. You need to specify a viewer for this: the default is ee.