How to turn off qq, Uni SMS and other software running in the background of Xiaomi mobile phone?

This is the problem with Android. Many softwares will start automatically, consuming a lot of memory and power. So the suggestion is that some useless and unnecessary software should not be installed. At the same time, I often clean up and close unnecessary software that runs automatically. I can find the running software in the settings, applications and software management of the mobile phone to stop them.