How to debug an android application?

Question

Java

I have an apk file from a past employee. There are no sources left. I need to track code execution. That is, at some point, find out the values ​​of some variables. I dismantled this apk first to smali, then to java. But how to debug it?
At least in which direction to dig?
I know that, like, you can write android:debuggable="true" in AndroidManifest.xml. And then how?

Answer 1

Next - turn on debugging on the device, connect the device, install drivers for debugging (sometimes necessary), and in AndroidStudio click Debug instead of Run. Well, of course, put breakpoints and other persimmons.