The iPad User Guide is a rich source of information about your iPad. Here is a direct link to the relevant section of the Guide:
Adjust the volume on iPad - Apple Support
As you’ll see, you can adjust the audio volume in several different ways…
1) the physical buttons on the edge of the iPad…

2) using the Control Centre, with a downward swipe from the top-right corner of the screen - then drag 

3) or, for system sounds, dragging the slider in iPad settings:
Settings > Sounds > [Ringtone and Alerts Volume]

You may find that you have greater control over your Ringer and Alerts Volume by setting Change with Buttons to OFF (as illustrated) - and controlling this element from the related slider control in iPad settings. This removes the possibility of accidentally changing your Alert Volume.