As you adventure, you earn experience (XP) by defeating foes, discovering locations, and completing other activities. Gaining XP allows you to level up, which in turn grants you one ability point. As you level up you can take on harder regions and enemies, revealing new quests that had previously been unavailable to you. Do not visit regions that are above your level range, as the enemies will be too difficult. The maximum level you can attain is level 50.
Assassin's Creed Odyssey eGuide The Essentials