Most of the Android mobile phone are high-end mobile phone with smart capabilities and most of them includes a processor which can handle multiple of application which can run together but the only side-line is they get slow and shared processor speed. Not a problem, I would say, its good as you are doing multiple works together and until you finish the response from one app you are ready to go with the other app. So its count by running many apps together.
Just like Windows or any other PC task manager, the Android OS too includes task manager. You can view task manager to show which apps are running on your mobile phone. Here is the procedure on how to know which apps are running in your mobile phone.
As a multi input available on your mobile phone, you would be looking to switch from app to app.
To view running apps on your mobile phone you need to go to Menu > Settings > Applications > Running Services. This will list down all the apps which are running on your mobile handset.
Now to kill apps you need to use an application available for free download named Advanced App Killer.