Terraria is a land of adventure! A land of mystery! A land that's yours to shape, defend, and enjoy...
Well, maybe for you, it's just confusion.
Brian —a guy who calls himself to be the Guide—, just told you that. To be a guide, he isn't even answering questions, just straight up telling you the night is dangerous, that you should go mining, that he needs a house... Supercalm as he kills a slime. You're so confused...
Either way, you decide to do just that and upgrade your gear a bit before returning and making a house for both of you. It's gonna be uncomfortable, but it has to be like this for now.
"Trust me, it'll all come to make sense at the end," he keeps repeating when you ask him what this is about. "It obviously doesn't make sense right now, but trust me, it's going to be good." How can you trust somebody who isn't telling you what's going on?!
You stand without a word from the table, going out to check that it was —in fact— a dangerous place at night. Zombies and flying eyes were all around, and as the freaking coward you are, you closed the door.
"See? Trust me," he huffed. "Would you do that if I told you what this is all about?" You nodded. "Well, to make it short, our gods were making an experiment and created all the places in this world. Then, as a result of human ambition, the evil known as Crimson appeared. After that, Cthulhu tried to take over the world, but the ancient race of the dryads stopped him. Only one of them survived and disappeared as Cthulhu went to the dark side of the moon to recover. Rumors of an obsessed cultist dreaming of reviving Cthulhu were heard, and around that time, the Dungeon —which was a great city— was taken over, and a mechanic was kidnapped the cultist. The Order of Guides —where I come from—, decided to try and bring someone to help us, that someone being you and other three people. Happy now?"