How to turn off unused apps on the iPhone?

Thank you in advance

On the iPhone, you press the home button twice, then you hold on the open app, it should start shaking and a red minus should come up. Press the red minus's

Your apps are closed.

If you mean delete them, hold them down until every app starts shaking. If a little X appears on the top corner, then tap it and its gone.
If an X doesn't appear then you can't get rid of it.

If you mean turning it off in a different way, then you can double click the home button at the bottom of your phone and a little row of apps you've used will appear. Hold those down till they shake and then you can delete those. They will not delete the apps, they'll just "turn them off" so to speak.

Double click the home button and a line of apps that are active will appear. Press one of the apps and hold until the icons start to wobble, and you will see a red button appear in the top right corner of all the icons. Press the red icon on all of the active apps to turn them all off.