GoKawiilChromeOS Flex requires an Intel or AMD CPU, 4GB of RAM and 16GB of storage. The age of the hardware matters too, since CPUs from 2012 or earlier don't support newer ChromeOS versions. Still, those are relatively modest requirements when compared to Windows 11.
You'll also need a USB flash drive with 8GB or greater capacity; everything on it will be deleted as part of this process, so be sure to back up any files if needed. Finally, you must have an existing computer with Chrome installed (download Chrome if needed) to create the installation media. This can be the device you intend to use for ChromeOS Flex, as long as it's currently functional.
After you've gathered everything you need, open Chrome and install the Chromebook Recovery Utility extension. Insert your flash drive into a USB port and open the utility via the Extensions button (which looks like a puzzle piece) located at the top-right corner of Chrome. Click Get started, then select Google ChromeOS Flex in the dropdown menus on the next page, followed by Continue. You should be able to select your USB flash drive and start the process at this point.
Once the utility has prepared the flash drive, insert the drive into the computer you want to install ChromeOS Flex on. Upon restarting or powering on this machine, you'll need to repeatedly press a key like F10, F12 or Del on your keyboard to enter the computer's boot menu — search your model online or check the manual if you're not sure which key to use. This can take a couple of attempts; if you see the Windows loading screen, restart and press the key sooner.
In the boot menu, select your flash drive (it may be labeled as something like USB: ChromeOS Flex) and wait for it to load. You'll be greeted with a setup wizard, where you can choose between installing the operating system or trying it out. The latter doesn't retain any data between restarts, so it's not meant to be used long-term. You might want to try it first to make sure everything works with your hardware.
When you're ready to install the new OS, be aware that doing so will erase everything on your computer, so make sure you've run a backup. After you choose Install ChromeOS Flex and the installation completes, remove the USB drive and restart the computer to begin using the operating system.