Do you know the steps to switching cellular carriers?

I ordered the new Pixel XL phone by Google, and I ordered a Project Fi SIM card to go with the new phone. Project Fi works in my area, and it is much cheaper than what I’m paying for cell service now with AT&T.

I want to keep my old number.

When I ordered the SIM card with the new phone, I thought it would walk me through the steps to set up the new service, but it did not. Does that happen after the phone arrives?

I’ve had AT&T for many years, so this will be the first time I’ve switched.

What happens next?