The Camp is a special feature of Baldur's Gate 3 (BG 3). When your characters use their spells slots, they need to rest at camp to refresh them. You can also interact with your companions at the camp, discussing the Quests, or advancing Romances.
Long & Short Rest
In order to take a Long Rest you'll have to gather Camp Supplies. Once you selected the "Go to Camp and end the day" button, located at the upper right-side of the screen, a message will ask you if you want to go to camp. You will also receive notice if you have or don't have enough Camp Supplies to restore all Hit Points and Spell Slots.
You can set up Camp anywhere now, as long as you are outside of combat and there is no visible threat to you. At Camp, you can proceed to interact with your Companions before clicking on the bedroll to go to sleep. A new menu will be displayed, in which you will be able to select either a Short Rest or a Long Rest. In order to perform a Long Rest you need to have 40 Camp Supplies.
A Partial Rest restores your Hit Points and Spell Lots to a certain degree, not fully, but doesn't spend Camp Supplies. On the other hand, a Long Rest, restores you fully, but consumes Camp Supplies.
Resting at camp will advance the in-game timer, causing certain time-sensitive quests to fail. (Some events will only be triggered after some rest, including Astarion suck your blood, Dreamlover scenes, etc.)
Possible bug: if you wake up at the camp during daytime, use fast travel or press the camp button again to leave.
Baldur's Gate 3 Camp Information
Can be invite to camp
The hooded skeleton you find in quest EXPLORE THE RUINS will appear in camp and provide revival services.
Scratch, the dog you find outside Blighted Village will also appear in camp, pet him to get the approval of your companions.
Volo, the storyteller will appear in the camp after you save him in Rescue Volo.
Barcus Wroot from quest Save the Grymforge Gnomes.
Raphael, a devil will visit you during one of the nights. And propose to remove the parasite in your head (Quest Removing the Parasite).
After several days of traveling, your dream lover (created in the Character Creation process) will appear in your dreams. However, that's actually the tadpole talking use the image in your brain.
After saving the druid Halsin and killing all of the Goblin leaders (Save the refugees), the Tieflings will hold a party at camp. You can invite one of your companions to spend the night with you at the party. (can greatly increase approval).
If you sided with goblins, the celebration will be a lot different, however, you may invite Minthara - the Drow Cleric - to spend the night with you.
Astarion may try to suck your blood during sleep, allowing him to continue earns you a lot of his approval.
If Shadowheart is not recruited at the Overgrown Ruins or the Druid Grove, she will appear on a random night. She will complain of voices telling her to find you and will attempt to kill you. She can be persuaded to not attack and can be recruited then.
After several nights traveling together, Gale will tell you about his situation. (Quest The Wizard of Waterdeep)