As you travel across the Forgotten Realms in Baldur's Gate 3, you'll discover a lot of people who want to join you, or who you can rescue. Several of these people will join you on your travels, but some of them will just be extremely grateful to you and stick around in your camp, and one of these people you might run into and rescue is called Volo the Bard.
Volo the Bard can be found in the Goblin Encampment, playing music for a drunken Goblin horde. You can rescue him by either sneaking into the prisons and persuading his captives to just let him go, or you can kill every single Goblin in the entire courtyard in order to save Volo, though this does come with the added issue that Volo might get caught in the middle of the battle and die.
Once rescued, Volo will meet you in your camp, but sadly as you'll discover from talking with the Bard, you can't get him to join you on your quest. He'll stay in your camp and every time you take a long rest you'll be able to talk to him and learn a little more about his backstory, but he'll never be able to join you in your fight against seemingly everybody across the entirety of this land.