"Settings" is the grey gear icon--it should be on your iPod's home screen.  You can disable your apps' background refresh from here. Background refresh is when apps you have open (but not active) refresh their information, either over data or via wifi. This eats up a huge amount of battery life. This will disable your apps' background refresh. Your apps should no longer refresh in the background.

Summary:
Open the Settings app. Find and open the "General" tab. Tap "Background App Refresh". Swipe the switch next to "Background App Refresh" to the "Off" position. Close your Settings app.