These cumulative updates to Visual Studio 2015 include a variety of bug fixes and capability improvements.

If you have Visual Studio Professional 2015 installed on a machine with Internet access, Update 1 displays in the Notifications Hub. To install, select the Update 1 notification, and then complete the installation actions. You can also download Update 1 here.

Visual Studio Professional 2015 with Update 1 provides professional developer tools and services to individual developers and small teams. Create applications for multiple devices, PCs, and the web, powered by the cloud and built on top of your existing applications and skills. Use cross-platform technologies to create applications for Windows, Android, and iOS from a single development solution and more.

Note: If you have Visual Studio Professional 2015 (original release version) installed and run the download from this page, only Update 1 is installed. If you don't have it installed and run the download, both Visual Studio Professional 2015 and Update 1 are installed. In either instance, Visual Studio 2015 Language Packs (original release versions) can also be installed.

VS Release Notes
TFS Release Notes
VS Known Issues
System Requirements
Compatibility