The Android device manager is accessible from android device, computer use web access and from your Google account. Generally, when people use android phone, they also have active Google account in this device. First to do is visit Google.com /android/ devicemanager using computer web site browser and look after to your device list. The device will automatically appear if you ever use Google Play Store with your device. Do not forget to rename your device for clarity and easier set enable android device manager. In default setting, the ring function is accessible. This option is for default ringtone in full volume. When this active and connect to internet, you are accessible to its location. For lock and erase function, there is special permission from Android Device Manager to android device.
Go to setting menu>click security> choose device administrator (This will determines who are allowed to access into sensitive Android device). Probably, when you installed additional security software or additional user account, there are multiple option appears. Just ignore and go directly to Android device manager. Check the box and click activate in lock and erase function. With this step, you are accessible to lock and erase function in android device manager site.
The Lock feature give access to new device password that very useful if your screen locks is ease to guess. This can secure your information when a thief efforts to access. For more extreme option, erase option will clear entire data in device and return it into factory setting. This will very useful if you have very important information in stolen or lost android device. However, keep in your mind when you use the option, your SD card information is still available to access just by plug your SD card to computer. Second, by clear the device, it also wipes everything that connects into your account. This means that you are unable to tract your device with android device manager. Therefore, choose the right option when you enable android device manager system.