Why, what, how. In that order.
Sprint Planning answers three questions. Teams that start with “what” end up with a list. Teams that start with “why” end up with a goal.
Why
The Sprint Goal
“What's the most valuable thing we can achieve this sprint?”
The Product Owner proposes. The team shapes it.
What
The Work
“Which items get us to that goal, given our real capacity?”
Leave, public holidays and support load included.
How
The Plan
“How will we build it? Plan the first few days in detail.”
The Developers own this part.
Source: Scrum.org / ScrumGuides.org: The 2020 Scrum Guide ↗
Why, what, how. In that order.