Need help about Android Studio

I would like to ask about the android studio.

Hai, I'm a newbie, just learning Android studio and programming recently.
I have a problem with the script/source code that I got from Github.

Here are my problems when I used Android studio.

1. When I created a new project (happy birthday card), it didn't show hello world in the virtual machine, it showed like when we turn on the phone for the first time. (Sometimes it showed "hello world", sometimes It's not.)

Note: I follow the tutorial as the developer android says. But unfortunately, I got that problem.

2. When I'm importing the script from GitHub (happy birthday card). It says that this source did not use Gradle. When I closed the app and created the new one, sometimes the script worked, but sometimes it did not.

3. Is there any setting that I missed in the android studio? And what about the Gradle, is there any way to automatically change the script/source code to using Gradle.

I need your help.
This is my first time learning programming and android studio. I just wish I could make apps myself. Even if it is just a happy birthday card app.
( I took a course from JetBrains about android development (kotlin) and took a course from developer android (google). Feels like my brain burst out.