how can I do this without usb or cd?

Your 2012 Mac should have three options in Applications -> Utilities -> BC Assistant.

• Create and Download - Use a USB2 Flash drive and a Windows ISO to build a USB installer for Windows.
• Install - Allows partitioning of your internal disk and complete the installation using the USB installer built via Create+Download.

What is the year/model of your Mac (do not post the serial number)? I assume you want to install Windows to use some software, which does not run on macOS.

Connect a USB2 8+GB flash drive. USB3 or USB HDDs do not work correctly.