Android apps are not normally closed when you switch between the android apps. Apps run in the background and are available to you when you open them again. Few android apps like GPS etc might use battery more and cause it drain. If you want to save battery or just want to clear the memory, you need to close all active or open android apps.
It is easy to close all active android apps in android. You can force all open apps at once to start fresh again. Android phones & tablets have Task Manager android app by default. You can use it kill all open android apps.
How to close all open android apps at once
1. Go to Applications > Task Manager on your android phone like Galaxy S2, S3 or tablet like Samsung Tab etc. If you don’t have default Task manager app like in Nexus 7 tablet, install Advanced Task Killer
2. Tap on “Active Applications” tab if its not already selected.
3. Tap on “Exit All” to force close all active applications on your android device.
You can also kill android apps individually on this screen. Using Task Manager, you can’t kill android processes & services like Maps, Movies, Settings etc
If you want to close or kill all or some of android processes at once, you can download Advanced Task Killer android app from Google Play Store. Uncheck items in non green text to kill open android apps. Remember, If you kill android processes, Android apps might not work properly.
Also, You can access Recent android apps you used using holding on home key or tapping on recent apps etc. You can close apps by swiping or closing in the recent apps list.
You can always reboot your android device If needed to clear any android processes or make it work normally.
Also, read how to setup parental controls & web filter on your android device