I am new to wp, I wonder if there is a way to show all the running apps as in Android. Does it depends on WP or on Nokia. Thanks
Holding down the back arrow to use the task switcher shows you apps that are open and you can kill them there if you're using Windows Phone 8.1 (in WP8.0 you need to spam the back button in each app). There isn't a list like Android's
Settings > Apps option.
First off, the only app "running" (besides background tasks, see last part) is the app you currently see on the screen. All other apps are being suspended and therefore don't use any battery.
Holding the back-button you will see a list of apps you've used before and which you can quickly resume as the phone will hold some necessary data in memory. The phone also discards these apps automatically if the list gets too big (I think 8 is the maximum current number of apps in the app switcher).
Lastly, there are APIs that can run some background tasks depending on your battery and Wi-Fi availability. Those can be found (and enabled/disabled) through the battery saver app.