"username" is the username currently logged in. So unless you add a user and log in as the new user, it would be "admin".
The first part of your quote from the manual is the path in the command line input. This is different because you told it to. If we assume you are logged in as admin then your normal command line path is
To import all the macros in the library file, you'll need to navigate to the macro pool. In the command line, type and execute (please/enter):
Now the command line path has changed:
This means that you are logged in as the user Admin and you are currently in the macro pool in the internal three structure.
Now type the command from the manual:
Import Library "*.xml"
Now you should have all the macros from the library file and you can change the command line path back to the root:
The * is a joker sign that can be used instead of the actual file name. The result is that the software selects all the relevant xml files and imports the content. Each of the macros are stored in their own xml file, so the alternative is to type the name of each file. The * joker just imports them all.