A hard restart can be handy and should be used if an app refuses to start or if your tablet has frozen up completely.
The reset process is simple, but will depend on which iPad model you have. If your iPad has a Home button, hold the Home and On/Off buttons together for a little under ten seconds, ignoring the Siri prompt that appears.
The screen then goes black and the Apple logo appears. Let go of the buttons and wait for the iPad to start up and everything should be back to normal.
If your iPad doesn’t have a Home button, the method is slightly different. Press the Volume Up button, then press the Volume Down button, and finally hold the Top button until your iPad’s screen goes black.