Anywhere you want, but traditionally there is a starting place. And it’s not where most beginning writers think it is.

The beginning should be where the action begins, which is to say where the protagonist first begins to interact with the story.

Most beginning writers want to put in a bit of introduction to either the main character or to the story itself.

Not a good idea because readers want to be immediately immersed in the story itself. Introductions can be inserted anywhere, anytime.