Turning-off the iPad is best achieved from iPad settings:
Settings > General > Shut Down
You can also shut down with a press-and-hold of the top button; when the on-screen slider appears, swipe to complete the shut down.
A forced-restart is a little more complicated. As your iPad doesn’t have the Home button, do the following:
- Press and quickly release the volume button nearest to the top button.
- Press and quickly release the volume button farthest from the top button.
- Press and hold the top button; do not release the button until...
- When the Apple logo appears, release the top button.

The iPad User Guide is a rich source of information about your iPad and iPadOS. Here is a direct link to the section that describes how to restart your iPad:
Force restart iPad - Apple Support