Unity 3D : Settings for Android build game.

If you try to set the Android SDK on Unity 3D using the Linux O.S. then you can have a problem.
After you set the name of the package and the default android settings you can use External Tool from menu Edit - Preferences to set paths for Android SDK, NDK, and more.
This is the path I used to build with Android:

• /home/catalin/Unity/Hub/Editor/2019.3.5f1/Editor/Data/PlaybackEngines/AndroidPlayer/OpenJDK
•  /home/catalin/Unity/Hub/Editor/2019.3.5f1/Editor/Data/PlaybackEngines/AndroidPlayer/SDK
• /home/catalin/Unity/Hub/Editor/2019.3.5f1/Editor/Data/PlaybackEngines/AndroidPlayer/NDK
• /home/catalin/Unity/Hub/Editor/2019.3.5f1/Editor/Data/PlaybackEngines/AndroidPlayer/Tools/gradle

You can see the android SDK, NDK and Gradle is set on the Hub Editor This is my External Tools configuration for that build game:

Unity 3D : The new learning area ...

The Unity 3D game engine comes with significant improvements in the learning area.
If you know nothing about Unity Editor and C # then this area has a simple and efficient introduction for new developers of this game engine.
For example , see the Creator Kit: Beginner Code.
You can start with John Lemon's Haunted Jaunt: 3D Beginner or with the Ruby's Adventure: 2D Beginner.
I am starting to see how deep and good these tutorials are and for me it was quick to follow them and use them.
This is an more advance learn step from Unity 3D using the Creator Kit: Beginner Code.