I am having a hard time figuring how to actually create or even open a DAC application with Visual Studio 2012. I am using SQL Server 2012. I have SSDT installed.
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The purpose of a DACPAC is to provide a portable representation of a database schema, that can be used to deploy that schema to a database, import it into a database project in Visual Studio, and be used in functions like Schema Compare to examine differences between different sources. Whenever you build a database project in Visual Studio a .dacpac file will be generated, and this can then be used to deploy the schema defined in that project to a database.
The best place for full information is the SSDT help, but I'll give you a quick summary.
If you already have a DACPAC, you can use it in VS in the following ways:
To create a DACPAC in Visual Studio, you can
Finally I'm not sure what video you viewed, but it's possible they showed right-clicking on a DB in SQL Server Object Explorer and creating a project from there. That's a very common way to start development using a database project, since often you'll already have a database containing your schema. Generally the best practices would be to develop using a project, and use dacpacs (and possibly command line deployment tools like SqlPackage.exe) when deploying out to different environments such as your production servers (again dacpacs are great for transporting schema definitions and deploying them to different environments). Hope this helps answer your question!