Installing and Using RSAT: Remote Server Administration Toolkit
The tools needed to manage Groups, Users, Computer Objects and other Active Directory resources are provided in a collection called the Remote Server Administration Toolkit, or RSAT for short. These tools are available for Windows 7 and Windows 8. (On Windows 7, installation of these tools is a two-step process. See below.)
Select the installer appropriate to your platform: either Windows 7 or Windows 8, and 32-bit (x86) or 64-bit (x64) versions of Windows. When you run the file, you will need to approve a security warning and possibly a User Account Control prompt.
Additional step required on Windows 7
Go to the Control Panel, selecting the "Programs" group, then under "Programs and Features", select "Turn Windows Features On or Off". On Windows 7, select "Remote Server Administration Tools" -> "Role Administration Tools" -> "AD DS and AD LDS Tools" -> "AD DS Snap-Ins and Command-Line Tools". On Windows Vista, From the list of features that appears, find "Remote Server Administration Tools"->"Role Administration Tools"->Active Directory Domain Services Tools".
Update: It appears that the "AD LDS Snap-Ins and Command-Line Tools" (shown below) must also be checked for for the tools to appear under Administrative tools.
The tools that most people need are included in the "AD DS Snap-Ins and Command-Line tools" option. Once that item has been checked, click OK and the selected tools will be added to your system.
Running the tools.
The "Active Directory Users and Computers" tool should now be listed under the Administrative Tools in the Control Panel. This is the tool used for group management.
You can right-click the icon in the Administrative Tools and select the "Pin to Start menu" option to make the icon always appear near on your Start menu.
If you have been given a domain account specifically for Active Directory management tasks, you may need to use that account to run the RSAT tools. You don't need to log into your computer with that account, though. Instead, hold down the "Shift" key when right-clicking the Active Directory Users and Computers icon, and select "Run as a different user".