The default file merge tool in the Visual Studio integration is Araxis Merge, an advanced two and three-way file comparison (diff), merging, and folder synchronization tool.
You can obtain help in Araxis Merge at any time by using the commands in the Help menu, or by pressing the F1 key. Some windows also contain a Help button.
You can change the default file merge tool to the Serena Merge Tool or any other third party application. For details see Configuring the Default Merge Tools in the System Administration Guide.