Enter the version string of your package.
Every build should have a unique version String.
You can use _$build_ anywhere in the string to get the unique Jenkins build id.
You can also use _$date_ to get the current date.
You can also use _$git_ to get the most recent git commit.
You can also use _$svn_ to get the most recent svn commit.
If you do not update the version number each build (either using any of the above options or manually updating the version) then submissions will have the same version and be difficult to destinguish in the user interface.