There are several ways to check what apps are running on an Android phone:

• From anywhere: Swipe up from the bottom of your screen to the top. If you get All Apps, tap it. Tap the app that you want to open.
• From shortcuts: Touch and hold the app. If you have options, choose one. Swipe up from the bottom, hold, then let go. If you’re on Android Go with 3-button navigation, tap Recent apps. Swipe left or right to switch to the app you want to open. Tap the app that you want to open.
• From Quick Settings: To open Quick Settings, from the top of the screen, swipe down twice. To see the number of active apps running in the background, look for the icon that shows the number of apps running.
• From Developer Options: Go to Settings > Developer Options > Running Services to see what apps are running in the background.
• From the Recently Used Apps screen: In Android 4.0 to 4.2, hold the "Home" button or press the "Recently Used Apps" button to view the list of running apps. To close any of the apps, swipe it to the left or to the right. In older Android versions, open the Settings menu, tap "Applications," tap "Manage Applications" and then tap the "Running" tab. Tap the app or process you want to close and then tap "End Process" or "Stop".
• From the app switcher or recent apps menu: If you have a newer Android phone, swipe up from the bottom-right corner of the screen. If your phone has physical navigation buttons, press the square app switcher button next to the home button. There may also be an icon with three vertical lines to access the app switcher. Swipe left or right with your finger to see all the open apps. To open an app, tap its image. To close an app from the Recently Used Apps screen, swipe the app window up with your finger. When closed, it disappears from the list.

Its important to note that some apps, like Google Play services or system apps, can’t be stopped.