installing windows on Big Sur

I'm thinking about installing windows on Big Sur in the future. I know how to use bootcamp assistant, and I've also listened to various podcasts demonstrating how to successfully install windows.
Question: after you check the "install windows 10 or later versions" option from within bootcamp assistant, it prepares the internal drive, then restarts into MacOS. how can I start the windows installation after mac restarts? any help could be great. thanks so much in advance.