This article will provide clear illustrated instructions on how to configure squid proxy access on different platforms. It should save us the trouble of explaining that to every user in proxy-enabled services such as Future School individually.
WARNING: if you are not sure if your Android device is rooted or not, there is a 98% chance that it's not. Proceed to "non-rooted device" section. If your device IS rooted, install ProxyDroid app from Google Play Store, it will allow you to configure the global proxy access on your device tied to a connection with a certain Wi-Fi network(s).
Unfortunately, as of Android version 4.3, proxy support is still not implemented fully as the inbuilt proxy settings lack username and password fields. It will work for your web browsers such as Chrome, Firefox etc. that are capable of displaying the username/password fields, but the rest of your apps won't be able to authenticate. There is no way to change that - your device has to be rooted to further tweak the proxy settings via 3rd party apps.