He finds builders and workers. He sets aside stones, iron, bronze, and cedar for the building.
Of course, David knows he won't be the one to actually oversee the building of the Temple. His son, Solomon, is. But Solomon is "young and inexperienced" so he'll need some help in order to make this the greatest temple the world has ever seen. God deserves nothing less.
David goes to his son and lays out his plans for the Temple. He tells Solomon that he would really like to be the one to do the work, but that God told him not to chance it. It seems that David has killed too many people (what with all those wars he was always fighting in). God can't have his house tainted by all that blood.
But Solomon will be a peaceful king and Israel will be a peaceful place while he's in charge. That's a way better time to build a temple.
David finishes by telling Solomon that he'll be successful if he always listens to God and stays faithful. (Spoiler alert: Solomon doesn't exactly follow through on this.)
He also asks the other leaders in Israel to stand by Solomon and help him. He's a good kid, but he's about to tackle a big project. Solomon will need as much guidance as he can get.