How can I understand what others say? Is there something behind the words? Or just talk casually

You have to grasp this yourself. At the same time, you need to look at the situation of others, who they are facing, what they say, and whether there are any interests involved? To understand what others mean, you can think about it from another perspective. If you were in the other person's shoes, would you say the same thing? If you compare it psychologically, you will understand a little bit. In fact, there is no need to take many things too seriously. The most important thing is to be yourself. Personal opinions are for reference only.