Located in the Control Panel, it provides both security and maintenance information for your system.
It also provides links to many other features such as backup settings.
You can reach it quickly by typing uac in the Instant Search bar.
This slider is set by default to a less annoying setting than what Vista had, but you can bring the settings back to Vista mode, leave it in Windows 7 mode (which prompts you only if an action is attempted beyond your input), or lower the settings to the bottom and turn off the UAC security altogether to what I like to call “Mac mode” (yes, I know the Mac’s UAC equivalent prompts users for the same kinds of actions as UAC’s Windows 7 mode). Note that the slider is also available in the Action Center.