Configuring Business Data Connectivity Services

Setup BDC with its own user, database and App pool
Start the service
You should have a pages host to contain the external content type definitions so you need to Configure /add an External Content Type Profile Page Host.
Create a new site collection (I use the same web application as the metadata hub created earlier)
Use the Publishing Pages Portal Template
Once published goto Central Admin ->Manage service applications –> Choose the BDC /BCS Service -> Click manage from the toolbar->Configure->Type in the URL of the site collection you created above. ie http://metadata.company.com/sites/ExternalContentTypesFinally assign administrators of the BDC Metadata Store by clicking on the Set MetaData Store Permissions.

To create external connections see this article