Google Play costs about 20€ to become a developer, Apple store is about 90€ (I think, it was around 90 last year).
For Google Play you need to export your project for Android Studio. Then unzip the exported files. Launch Android Studio as administrator and open the project (files you just unzipped). Fix any errors - for most things Android Studio will tell you how to fix. Right click on app, go to Module settings, select app, go to Default config tab, enter Version Code and Version name (for example Version Code is 1, Version name is 1.1). Go to Build, select Build variant, select Release. Go to Build, select Generate Signed Bundle or APK. Select Android app Bundle, follow the steps, enter your key information. Wait for the build to finish and the locate the file.
In google Play console, if this is your first app, click on any of the "create new app" buttons. Upload the file Android Studio has created and enter all the information. You need to fill out all questionnaire, upload screen shots etc. before you can start any testing. Once you've done everything wait for the app to be published (takes about 2-3 days) then go back to the test you have started when you uploaded your app (for example, internal testing) and you will get the link to share to your testers.
I hope this is what you wanted to know :)