The Raspberry Pi is getting a massive upgrade. Now, you'll be able to install an operating system to the affordable computer without needing a second PC to get it up and running.
Before this update, you needed to flash an operating system of your choice to an SD card, which allowed your Raspberry Pi to boot. Without that process (or buying an SD card with a preloaded operating system), there was no way to get your Raspberry Pi running.
In a blog post, though, Peter Harper from Raspberry Pi said, "The new Network Install feature can be used to start the Raspberry Pi Imager application directly on a Raspberry Pi 4, or a Raspberry Pi 400, by downloading it from the internet using an Ethernet cable." That means you can connect your Pi through ethernet and install the operating system onto a blank SD Card.
As far as what operating systems you can run, Raspberry Pi posted a full list, and most of the major distributions are available.
The network install tool is currently in beta, and you can test it out right now. It's a bit of a process to get it up and running, as you'll need to download the new beta bootloader. The blog post by Raspberry Pi breaks everything down in detail with screenshots that'll help you run through the process.
Eventually, this feature will leave beta and come to all Raspberry Pi 4 and Raspberry Pi 400 devices, so you won't need to go through the beta process. This is a massive game-changer for people getting started with the Raspberry Pi, as it removed one of the barriers to entry.