because there is wide variety of subjects to tutorials this form is designed to fit them all.
For example if you are doing Flash tutorial it's common to provide startup file, and resulting file for those lazy ones
. Those fields are not mandatory because you can write a PHP or Ruby tutorial where you don't want to add startup or resulting file.
Preffered file format is just any type except .exe or something like that (executable), so if you have 3 or less startup files upload each of them individualy, or if you have more than 3 you can zip them and place just one startup file.
Resulting file is only one so if you have more than one you can also zip all that in.
Hope this helps,