Microsoft seems to have two products called SSDT (SQL Server Data Tools)
1. A development environment for SSIS etc.
2. A source control tool that uses TFS.
To install 1. You choose SSDT as an option whilst installing SQL Server 2008r2 or 2012.
To install 2. It is a separate download for Visual Studio 10 and 12, or a post installation option for Visual Studio 13.
(SSDT is really just a badly integrated set of tools. I find treating it as two distinct products keeps me sane whilst googling)