If you're a newcomer to Windows 8, and having trouble getting a feature to work, then scanning the official Help files might prove useful. Open the Charms bar, click Search, and type in 'Help'. Help+Tips is a Windows 8.1 app with some useful, but basic information, while Help and Support has more in-depth advice.
If you're an expert PC user though, or the problems are more severe, then consulting the usual Control Panel applets may point you in the right direction. Action Center may reveal problems Windows has noticed already, Device Manager and Event Viewer often highlight relevant low-level issues, and the Troubleshooting applet has a wide range of fixes to offer.