The world of Mabinogi
Although often referred to as Mabinogi, the actual name of this world is Erinn. The world consists of two large continents: Iria in the east, and Uladh in the west, and has two moons. Erinn is a world of magic, monsters, alchemy and fighting.
Rebirth
Your character is not a native of Erinn, and will be born and reborn through the Soul Stream. The Soul Stream guides souls to the world of Mabinogi. This happens when you are first "born" into the world, and will also happen every time you are reborn. In Mabinogi, you can choose to undergo the rebirth process, which will let your character reincarnate into a new body, while keeping your old skills, equipment and titles. You can change your appearance, age, and even your gender.
The races
As a player, you will have the option of creating a character of one of the three main races: human, elf, or giant. Humans are well-rounded compared to the other two races. Elves are smaller and weaker than humans, but are better at archery and magic. Giants are larger and stronger than humans, making them better at physical combat but worse at magic and archery.
Age
When you create your character, either for the first time or during rebirth, you will choose their age. You can create a player as young as 10 or as old as 17. As a character ages, they will increase their stats, as well as changing physically. As your character gets older, they will get stronger.
What to do
Mabinogi allows you take part in standard MMO activities like raiding dungeons, completing quests and fighting other players in PVP, you can also write music, create clothes, learn alchemy, get a part-time job, or just socialize with the other players. If you want, you can even avoid combat altogether and focus on non-combat activities and skills.