How to manually install gradle for Unity2018.4.14 personal

I am a beginner and I came up with a problem in building. I am using Unity 2018.4.14 personal. There is no option in Preferences->Externals called Gradle. I have to install it manually. But I don't know how to make it. I had tried some ways such as put the gradle Folder in Unity/Editor/Data/PlaybackEngines/AndroidPlayer/Tools. But when I build, there will be errors.
Is there a complete way to install Gradle and Gradle android build tool and (something I do not know but need to be installed before building)