An example of when to use hans/hendes/dens/dets would be something like this "Han hjælper hans/hendes mor" meaning "He helps his/hers mother". In this case it is helping someone elses mothers. To be honest, many if not most, Danes also struggles with this grammatical principle. If I were you, I wouldnt worry too much about it. Most Danes cant see when it's wrong anyways. Use what feels right to you and if it's wrong, you will get corrected and over time you will get a sense of when to use what. That's unfortunately the best advice I can give :(

Salut :) Following are two examples which should help you understand. The situation is as follows: Peter is an author, and his friend is called Mette, and she is also a writer. Peter læser sin bog < this means that Peter is reading his OWN book (i.e. the book Peter wrote) Peter læser hendes bog < this means that Peter is reading Mette's book Mette læser sin bog < Mette is reading her own book (i.e. the book Mette wrote) Mette læser hans bog < Mette is reading Peter's book same with dens and dets. The key is: if you would use OWN in English, then it's SIN. For everything else (...) there's hans/hendens/dets/dens Alessio