You have your premise, and hopefully, a nugget of a conflict.
You know your main character a little more than you did a few days ago.

Ordinary World
Now we need to sell the reader on why they should care about your character and the conflict that character is about to face.

IMPORTANT DISTINCTION:
You are defining the "beginning" of the story chronologically, where everything in your character's life is familiar and ordinary, before their life is upended by the conflict described in your premise. This is not necessarily the beginning of your novel. Not every story is narrated chronologically. But you still need to know your character's ordinary world so you understand how they will react to the conflict and complications thrown at them along the way.

3 Reasons You Need to Show Your Protagonist's Ordinary World  

Inciting Incident
This is the event, brought about by outside forces, which kick-starts the character's story, urgently uprooting them from their ordinary world and throwing them into conflict.

Examples of inciting incidents from well-known novels  

IMPORTANT DISTINCTION:
The inciting incident is not always the first thing that happens, either chronologically or narratively. However, it should happen early in the narrative.

Cheers,
Michelle