Wow, that’s a lot! Let’s break it down.
Our Connections collection has a single entity in it, an OLE DB Connection named Adventureworks (remember, all of this is case sensitive so this Adventureworks is a different beast from AdventureWorks, ADVENTUREWOKRS, etc). This provides enough information to make a database connection. Of note, we have the server and catalog/database name defined in there. Depending on the type of connection used will determine the specific name used i.e. Initial Catalog & Data Source; Server & Database, etc. Look at ConnectionStrings.com if you are really wanting to see how rich (horrible) this becomes.
There’s a lot of XML to describe a single table, but a key benefit to Biml is that you write templates and scripts to generate this stuff rather than typing it out.