build without spending the premium prices for bleeding edge stuff, but will definitely get the job done including being able to play modern games well. Do you already have a monitor, kb/m? Putting together a pc is easy to do these days, I recommend watching some build videos on youtube ahead of time with your son, I really like Linus Tech Tips, though there is occasional language if you are concerned about that. As for windows, I would recommend setting up a USB drive with windows ready to install on a computer ahead of time. When you boot up the PC you should see it "POST" which is where you will see an icon/display from the motherboard vendor (ASUS) and you will push the DEL key to enter the BIOS. In there you can set some things such as the boot device, in this case you will want to make sure it is booting to the USB and then windows setup will come up and take you from there. Other settings to look for in BIOS, you will want to make sure some XMP profile is set to get full speed on your memory, you will want to make sure after windows is installed that your boot device is your NVME, and you will want to turn on UEFI boot (might be the default). Good Luck!