Can I kill background apps in my android phone?

They both should do the same thing, but I've seen some people say online that Force Stop can sometimes work when kill won't work. But you actually don't need to do either...

Android automatically kills apps that haven't been used recently if it needs memory for new apps, and it runs the same whether it has a lot of available memory or only a little. Killing apps yourself won't make your phone run better, and actually can cause problems if you kill apps that need to be running.

Anyway, many background apps will automatically restart even if you kill them, and setting up a task killer to constantly kill them will not really help things since now you've added another background app (the task killer).

U can restart ur phone or u may use a task manager available at play store

Yes u use the task manager