Per the Wall Street Journal:
During their private White House meeting on Thursday, Mr. Obama walked his successor through the duties of running the country, and Mr. Trump seemed surprised by the scope, said people familiar with the meeting. Trump aides were described by those people as unaware that the entire presidential staff working in the West Wing had to be replaced at the end of Mr. Obama’s term.
After meeting with Mr. Trump, the only person to be elected president without having held a government or military position, Mr. Obama realized the Republican needs more guidance. He plans to spend more time with his successor than presidents typically do, people familiar with the matter said.