How to format and reinstall the inbuilt Wiindows 10 on Laptop Spin SP513-51

Hi,

The storeman said that I don't need a Windows 10 installation disc as the OS is inbuilt on this laptop Acer Spin SP513 and I can format and install Windows 10 from the laptop's reserved disk for Windows 10.

If I format via Windows 10, how do I install Windows 10 and won't it ask for a product key number?

Thanks so much in advance for some easy steps to follow.

Cheers,

Ithan