The Volume controls allow you to set the volume for various sounds that your device can make.
The volume control is split into different settings for different types of sounds. The categorizations vary between devices, but commonly consist of the following.
Common volume controls on Android devices
The ring volume refers to the volume of the ringing when you receive a call.
Controls the volume of alarms you have set up in the Clock app. If you device does not have this option, you should be able to control alarm volumes for your alarms separately in the alarms section of the clock app.
Called Music & videos on some devices, this control adjusts the volume of normal sound that is generated by your apps, such as sound from video and audio playback, by websites or by games.
Volume controls that may not appear on all devices
This adjusts the volume of the message tones when you receive a text message or other notification for which you have enabled sounds, such as an incoming email. Note that if you want to control which types of notifications generate sounds, you need to do this within the respective app. For example, email notification sounds should be enabled or disabled in the email app.
On newer versions of Android this volume control is often combined together with Ring volume, preventing the ringtone and notification volume from being adjusted separately. Some devices include a checkbox allowing you to choose whether to combine these two volume controls into one.
Controls the volume of various little system sounds such as the pressing of keys on the keyboard. On some devices this option may control the noise made by the camera shutter. Some devices may not have this option, and "system" sounds may just fall under another volume setting such as the Music & videos volume setting.