David did not announce who was to succeed him. Because of this, there was fighting between David's sons over who should be king. Adonijah invited guests to a banquet and declared himself king. Then those favoring Solomon told David and he declared Solomon the new king.
Several times in this chapter, the people use the idiom "sit on the throne" to mean "be king." Solomon assures Adonijah that if he behaves himself "not a hair of his will fall to the earth," meaning "he will not be harmed." (See: [[rc://en/ta/man/jit/figs-idiom]])