On this page of the Valheim guide you'll learn the purpose of the stone oven.
The stone oven was added to the game in the Hearth And Home update. It's used for only one thing - baking food. Dishes such as bread or Lox Meat Pie are no longer prepared entirely in the cauldron.
Instead, by the cauldron you create their raw, inedible version. To be able to eat the dish, you need to process it in the stone oven. To build an oven you need:
- Iron x15
- Stone x20
- Surtling core x4
Additionally, you must have the artisan table unlocked. This means the oven becomes available only in the later stages of the game.