What doe that mean concretely?
Playbooks is an aspect of PotA I haven't really dove into. I do own Beyond the Wall but haven't got to read it yet.
1) You pick a playbook, such as Devout Acolyte, Fae Foundling, or New Guardsman. Each playbook specifies a specific class for your character (either Warrior, Rogue, Mage, or a multiclass). The playbook will also specify a starting array of stats, usually 8s and some 10s or a 12.
2) The playbook has 6 questions for your character, and a table for the answers (usually 6, 8, or 12 possible answers). As an example, the first question in the Devout Acolyte playbook is "What did your parents do in the village? What did you learn from them?".
If you roll a 7, the answer is "Your parents ran the local inn. You grew up meeting many travellers and hearing their tales.", which gives you some background info, and adds +2 to Cha and +1 to Int, Dex, and Wis.
On a 5, the answer is "Your father was the local smith and taught you both hammer and bellows.", and you gain +2 Str, +1 Dex and Cha, and the Smithing Skill.
3) Each playbook also has one question where you share backstory with another player. As an example, the Devout Acolyte has this question: "When you were most in need, the gods aided you. When were you most desperate?
The player to your right was there with you."
If you roll a 6, the answer would be "A strange, small man with knotted skin was attacking those who came near the old mine. You
confronted the creature, holding it at bay while your friend struck it with iron and sent it running.
The friend to your right drove off the creature, and gains +1 Int.", and you would gain +2 Int and the Mystical Shield spell.
4) The playbook also gives basic rules like starting hit points, attack bonuses, saves, etc.