What is marriage in PNG context?

In PNG, what does it mean when one says he or she is married? when is marriage recognised? What I want to find out is, is it just living and having children with the opposite that people say they are married to that person? I wonder if there are some laws that regulate legal marriages, or is it people just come together and claim they are married.

If in the case of break up in such situation, do you refer to the law even if the law doesnt recognise your marriage? Or if you find out that your so called husband or wife is having an affair with another woman or man, what happens, do you go to the courts. The thing here is you are not married in church or signed any marriage certificate. What happens, what will be the outcome?

Please give true and helpful info on this

Thanks

Gibbs