Unlock your first skill

Defeat an Elder Guardian.

Kill a Mob while wearing the same type of Mob Head.

Dry a Sponge in a Furnace.

Eat a Notch Apple.

Create and fully power a Beacon.

Spawn the Wither.

Kill the Enderdragon.

Gain the trust of an Ocelot.

Use a saddle to ride a pig, then have the pig get hurt from fall damage while riding it.

Brew a potion.

Travel by minecart to a point at least 500m in a single direction from where you started.