Is it possible to start a process instance from a web application

I have the following situtation:

1 - A web portal of an organization has a feature that records customer orders;
2 - Whenever a request is received It's necessary to start an organizational process to treat the order generated;

What It's already done:
1 - The web portal already exists;
2 - We designed a process to treat the order;

Now I want do link both in a way that every order generates it's own process instance.

The process begins with a message event to receive the order, but what I'm still trying to figure is how I link the order generated in the web portal to the message event (synchronously), or if It is not possible, I need do know another way to achieve the same result.

Does anyone has a exemple?!

Ps.[1]: I'm talking about this particular case, but I already have other needs pretty equal.
Ps.[2]: I though about using a webservice, but I don't know to configure it at the process definition/ cofiguration to make it work.