Include, one cannot live without the other. The use case 
must include another use case. For example when you create 
an order you always must verify name etc. 

Extend, one can live without the other only some instances 
the use case will extend to another use case to do some 
stuff. For example, you can create an order but if the 
order is for a new customer you possible have to do 
additional check which you do not have to do for existing 
customers. In that case you can have an extend use case.

For Component:- A Component may use interface called import
                A Component may realiase from interface 
called export

An Extends relationship is exactly like an Includes
relationship with one important difference: An Extends
relationship is a conditional include

Include: Can not be completed without the included use case. For example To order an item, one must select the item while extends is executed on an particular event for example View Report extends print report.

Extend - if a use case is optional for another use case. 
that is defiend using extend; if a use case should be 
called another use case to accompalish a functionlity ,it 
will be represented as include.