I am not familiar with the term use case, is that related to UML?
This is a UML related term. In simple words, this is the name given to the element that is being added to your project. e.g. If you are adding a new action to the struts-config.xml file, you will have to give the action a name. It cannot be left blank.
I noticed the tutorial has left out the use case empty and go straight into the path textfield.
Which section of the tutorial are you referring to ?