You can use any player options from the D&D 5th Edition Player's Handbook, Tasha and Xanithar's books, Volo and Mordenkainen's monster books, or Fitzban's dragon book.
Generate your Attributes by rolling 4d6 and dropping the lowest die. Do this 6 times.
Lineages
You can use any lineage (race) from the player's handbook or choose an option from here.
Hometowns
Everyone's from somewhere - figure out where your character grew up by browsing the Lands
Faiths
Does your character believe in the Gods? Do they worship any diety in particular? Learn about the higher powers of the realm here.
Build your own lore
It's all totally up to you, so write any backstory you want for your character. Let me know if you want anything added to your character's Adventurers page or if you want to fill in some world lore.