Visual Studio Extension Manager is a feature that lets you add, remove, enable, and disable Visual Studio Extensions. Visual Studio Extension Manager allows you to install custom extensions along with 3rd party extensions and templates. To access the Extension Manager you follow the menu-item off of the Tools Menu.
The Extension Manager window is divided into three panes. The Left pane lets you select by group:
The extensions in the selected group are displayed in the middle pane. You can use various filters to sort the list. When you select an extension in the middle pane, information about it appears in the right pane. If the extension is not installed, you can download it; if it is already installed, you can uninstall it, enable it, or disable it.
The Extension Manager window also includes a search box. Depending on the selection in the left pane, you can search installed extensions, the online gallery, or available updates.
Extension Manager can install extensions from the Visual Studio Gallery (http://visualstudiogallery.msdn.microsoft.com/en-us) on the MSDN website. These extensions may be packages, templates, or other components that add functionality to visual studio.
When you select an Extension in the middle pane you will get an option to Download it if it is not already installed.
Otherwise if it is installed you can Disable it, Enable it, or Uninstall the extension.
If we click on the download link you will be either directed to an Agreement for Installation or to a third party application for installation.
For the integrated packages from the online gallery - you will be prompted to restart visual studio after successful installation.
In the case of the above extension, I installed spell checker for comments and plain text. After Restarting Visual Studio, I am able to immediately start using the extension
And here is choosing the option of what to do with the Mis-spelled word(s).
More information on the Visual Studio 2010 Extension Manager can be found on MSDN. http://msdn.microsoft.com/en-us/library/dd293638.aspx