Assuming Windows 7 is your OS: Go to Control Panel->System->Advanced System Options->Advanced->Environment_Variables(button near bottom).
You should see at least three variables there: PATH, TEMP, TMP
Click on PATH, click edit.
Scroll to the end of whatever PATH variables are already set. Don't modify them. Add a semi-colon (";") to the end, and then type/copy-paste/whatever the exact path to the 'bin' subdirectory of where you installed git. For example: "C:\Program Files (x86)\Git\bin\"
Apply the changes, and CMD should now run git commands.
By the way, this procedure is what you should do to also get other commands to run directly in CMD terminal as well.