I .
1.
to get into a comfortable position, either sitting or lying :
I settled down with a book.
2.
to start to have a quieter way of life, living in one place :
When are you going to get married and settle down?
II .
settle down | ˌsettle sb ↔ ˈdown
to become or make sb become calm, less excited, etc. :
It always takes the class a while to settle down at the start of the lesson.