That way you don't have to delete any Microsoft accounts as you will be starting from fresh.
Cortana is your assistant who will answer questions for you etc. Best to answer them yourself !!
If it has Win 10 already installed then you don't need to enter a key during install as it will auto activate when you connect to the internet because they keys is digital and saved in the cloud on the Microsoft servers.
This forum has lots of tutorials about all sorts of Win 10 stuff.
You don’t need discs with Windows 10; you can do a clean install online.
(Or you can create your own discs using a machine that already has Win 10 if you want to put it on a brand new setup).
Sorry I can’t link it from here but search for “Update Assistant” or “Microsoft media creation tool”.
You will need a valid digital licence.
If your machine already has Windows 10 it’s licence is stored on Microsofts server for that machine/motherboard and you won’t need to enter it again, even for a total clean reinstall.
If it’s a new build and/or first time instalation of Win 10 then you will need to buy a key/licence and enter it.
When you buy Win 10 that’s usually all you get anyway, a licence number and a link to the MCT (no disc).
As this is a 'refurbished' machine then you may want to run something like Malwarebytes ADWcleaner, which can remove any advertisingware, junkware, and other Potentially Unwanted Programmed (PUP's) that the reseller may have put on there as a 'bonus' for you.