One of the new features in Windows 8 is notifications and you can be alerted to certain events that take place. For example, Start screen apps like Alarms, Calendar, News and others can display pop-up messages informing you of something that just happened. Sometimes, though, you just don't want to be disturbed and you can suppress notifications temporarily.
You don't need notifications when you are asleep for example, and you might need to work without interruptions, such as when a deadline is looming. Switch off notifications until you wake up or have the time to deal with them.
If you are working on your PC, go to the charms bar at the right side of the screen (press Windows+C) and click Settings. Down at the bottom is Notifications and clicking it shows a simple menu that lets you hide notifications for a short period of time.
You could hide notifications for eight hours if you wanted to leave your PC running while you are asleep (the middle of the night is a good time to download big files), but you are bound to forget some time and then you might be woken by notifications.
It is better to set quiet hours. Go to the charms bar again and this time click Settings, Change PC settings. Go to Search and Apps, Notifications.
Turn quiet hours on and set the times, such as midnight (0:00) to 7.00. There is an option to receive calls - Skype calls presumably - and this is your choice. If you don't need to receive calls at night, turn it off.