Download the Debian 11 installation image from the official website.
Create a bootable installation media from the installation image file, such as a USB drive or CD.
Insert the installation media into the installed target system, set it correctly, and boot from it.
When prompted, partition the hard drive and choose the options that meet your needs.
Find the package you want to install, such as the desktop environment and additional tools and utilities. Select Install and press enter.
Wait for the installation to complete.
Configure the GRUB boot loader to boot Debian as the default operating system when prompted.
Finally, log in to the system using the username and password you specified during installation.