Hello
Janwid - welcome to the forum!
Your question has several answers depending on what you are wanting to do? The simple answer, is that if an app is open on your home screen, press the 'Home Button' once at the middle bottom of the iPad (when held in the portrait position); the open app should close and reveal your home screen.
Now when apps are closed in this fashion they are put into a 'suspension mode' using little resources but can be re-opened quickly to where you left off - to see which apps are kind of 'resting' in this mode, press the 'Home Button' twice (quickly); a task bar will open at the bottom of the home screen showing the 'suspended' apps - press and hold on any of the apps - all will soon start to jiggle; there will be a red circle in the left upper corner of each app - press that circle and the app will be shut down - this maneuver might help to correct a misbehaving program.
If these suggestions do not answer your question, please re-post to this thread - good luck!