This verse describes the aftermath of King Josiah's fatal encounter with Pharaoh Neco at Megiddo. Let's break it down:

"So his servants took him out of the chariot...": Josiah was wounded in battle, and his servants removed him from his primary chariot. This shows the severity of his injuries.

"...and put him in the second chariot that he had...": This implies that Josiah had a secondary, perhaps more comfortable or secure, chariot designated for situations like this. It suggests a level of planning or preparedness for potential injuries.

"...and brought him to Jerusalem...": Despite being mortally wounded, Josiah was transported back to Jerusalem, the capital city and the seat of his power. This shows the importance of bringing the king back to his people and his royal city, even in death.

"...and he died, and was buried in the tombs of his fathers.": Josiah died in Jerusalem after being brought back from the battlefield. He was buried in the royal tombs, indicating his status as a king in the Davidic line. The mention of "tombs of his fathers" emphasizes his lineage and connection to the great kings of Judah's past.

"All Judah and Jerusalem mourned for Josiah.": This signifies the great respect and love the people had for Josiah. His death was a significant loss for the nation. This mourning likely stemmed from:

His righteous reign: Josiah was known for his religious reforms, his destruction of idols, and his reinstitution of the Passover. He was a king who sought to obey God's law.
His protection of Judah: He was seen as a protector of the kingdom. His death left them vulnerable.
The loss of a good leader: Good kings were rare, and Josiah's leadership was valued.

In essence, the verse conveys the following:

Josiah's death was a significant event.
He was treated with respect, even in his death.
He was mourned deeply by his people because he was a righteous king who had served them well.
His death was a national tragedy.