Hi,
Web services are used when you want to allow multiple ussages of diffrent subset finctionalities.
For example if you provide a webservice to find what is the number of remaining seats.
This webservice is a complete business flow and can be used in various other applications to show from your system how many seats are still available, i.e even out side of you application.
If you are familiar with Remote Function CAlls Webservice is just the same wiith additional infrastructure to support authentication, discoverability, ease of use, etc etc.
It would be good if you read through
a simple enoguh intro thru:-
http://www.w3schools.com/webservices/default.asp
the main idea is to have enterprise ready systems ready for integration and is the way of now and the future.
For your simple project i would advise you to use REST style webservices rather than the Bulky SOAP implementation.
So just google around and you should be happy.