'It's hard to explain' signified that there was going to be a long story inbound.
Song Shuhang immediately made a listening gesture to show that he was getting ready for the Great Northern Emperor to tell the story from the ancient era.
In fact, Song Shuhang really loved listening to gossip about the ancient era.
The Great Northern Emperor said, "Well, I guess I can summarize it in two to three sentences."
Song Shuhang: "..." Senior Beifang, can't you follow the script?