Not 100% sure this is what you're asking, but it looks like you're having trouble instantiating a new loan object from within a method of the librarian class so you can return the loan object from the method?
If so, the piece you're missing is this:
loan l1 = new loan();
After you instantiate the loan with that code, you can then call setters on the loan (you have those I trust?) to initialize the loan.
Note that if the librarian and loan classes are in different packages, you will need to import the package containing the loan class in librarian.java!