I ned help with Android phone's best-kept secret.

[Geek-9pm]

Introduction.

I med help with Android phone's best-kept secret.

Many would say the Apple iPhone is the best choice you can make.
Well, even if that is true, you may want to get and Android and your second phone.
Here is why.
Reference:
https://www.greenbot.com/article/2090541/why-you-need-to-start-using-google-voice-your-android-phones-best-kept-secret.html

With an Android phone yu can make full use of the Android Apps that let you do voice over Wi-Fi instead of going through you cell service. Google voice lets you use an Android phone to call over Internet using a Wi-Fi connection. This will free up your first phone for important calls while you chat with your mother over a VoIP connection using the Google voice thing.

Now about my problem.
It is not hard to do, but I have a question or two.
What do you do when you mess it up?   
 
I did mess up. I know my Google number, but I have to reset my Android phone and I don't know how to again associate my Android phone with my Google voice phone number.
Whenever I call using my may Google  phone, it does not answer. Nor can I make calls from it.
I have tried going into the guides Google has, but I can not fin done for my specific problem. 

It used to work. Then I had to reset my Android device. Now it does not work.
Please help me. I am so frustrated.