how can i download windows

You need to purchase a a license from Microsoft, then they'll provide a download link for you to get the Windows Image you can then install on your Mac.

See here: Purchase Windows 10 - Microsoft.com

You can then choose to either use Bootcamp to install it, or use a virtual Machine such as Parallels, VMWare or VirtualBox.

See here: Install Windows 10 on your Mac with Boot Camp Assistant - Apple Support

here: https://www.parallels.com/products/desktop/

here: https://www.vmware.com/products/fusion.html

or here: https://www.virtualbox.org/wiki/Downloads

See:

Install Windows 10 on your Mac with Boot Camp Assistant - Apple Support

from that:

download a Windows 10 disk image from Microsoft.

You can install Windows using Boot Camp Assistant: Boot Camp - Official Apple Support

or using a virtual machine like Parallels, Fusion, or VirtualBox.