App Killer app that force stops apps needed

[AC Question]

I am in need of an app, an app that (without root) kills (force stops) apps I want, becuse they always run in the background and I cant make them go away (or can I? does anyone know a way?). This app also needs to stop killing the apps I select when I enter them, and continue killing them when I exit them. If there isnt an app like that, prehaps someone can help me by writing (in detail) how to stop some apps from starting when I turn my phone on and from running in the background when I clearly am not using them.
Thank you in adv.
My phone specs are Android 5.1, 1.5 GB of RAM, MTK6735 64bit quad core 1.0GHz

 

[belodion]

Consider Greenify. There may be other apps like it: I don't know.

 

[ManiacJoe]

The important details missing from the question would be the list of apps you want to kill.
Many of the services (not apps) running in the background are not optional.