What is Microsoft BizTalk actually used for?

Solution 1:

Biztalk allows applications to talk to each other. It is used for sharing information or events between applications or systems that are needed to work together in a business process.

It provides a way of mapping inputs and outputs of different systems, for example when they use incompatible protocols or formats. I believe this is done in XML. It also provides collections of scripts or procedures, called orchestrations, that allow a set of actions to occur in target systems when triggered by something happening in another system.

It's an implementation of an enterprise service bus, which is a platform for building a service oriented architecture - if that helps...

Solution 2:

To understand better the concepts of enterprise application integration I highly recommend you this book.

It gives an overview over all patterns you will see, and some input about the different competitor of the market (Tibco, Biztalk, and something from IBM I forgot the name).