How to become a citizen in Germany

I'm in Vietnam. my girlfriend is a native of Vietnam, but had moved to Germany. I really want to go to Germany, but do not know how to be recognized as citizens in Germany. Please people show me how to be recognized as citizens in Germany. I am currently living in Vietnam. Thank you very much for your help

You have to live 8 years in Germany before you can apply for citizenship. If you show good progress in integrating into the German society, this can be shortened to 7 years.
There are exceptions (e.g. for people of German ancestry or those seeking political asylum) , but for most this is the rule.

Thank you for your help! I will probably never become a citizen because I was not in virtue ethics