Because of various incidents, Walt and Thao and Walt and Sue gets to know one and each other and relationships are built.
The movie consists a lot of racism between ethnic groups, especially between "white" and Asians. From my opinion Hollywood often portray people of different races as enemies and there is often a lot of violence, guns and swearing. Kind of mafia like with threatening of families ect. I think Hollywood often overdo it when making movies.. At least so I hope.
It can be really hard to be an immigrant, because you need to be able to become a part of the new society and you're also dependent to be accepted by the new society. It is also very important that you do an effort yourself; to learn the new language for example. Also you have to accept the new society and their traditions and morals.