I know it is too late to ans, this ans is for those who are trying to google to look for some answers.
The difference between extend and uses is
uses is "has a" relation while as extends is same as inheritance "is a" relationship
One simple example is
Use case (Check In A Passenger) this use case has 2 other relations associated with it. (Weight Language) and (Assign A Seat) When we want to define relation between then we will use <<uses>> (Assign Seat) has 2 more use cases. (Assign Window Seat) and (Assign Aisle Seat) These 2 will be shown as <<extends>> because window seat and aisle seats are/is seats.
Hope this helps