Here the phrase "all Israel" represents the entire Israelite army. AT: "David and all the Israelite army" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The word "now" is used to mark a break in the main story line. Here the narrator tells background information about Jerusalem. (See: [[rc://en/ta/man/translate/writing-background]])
Here the word "took" is an idiom that means "captured" or "conquered." Since David led the army, his name here is a synecdoche for the whole army who attacked the city. AT: "David captured the stronghold of Zion" or "David and the Israelite army captured the stronghold of Zion" (See: [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-synecdoche]])