Bitwarden’s generator is a web page that builds a random password or passphrase in your browser. You set the length and the character set, then you copy the result. You do not need an account. The useful version of this is local: the page should be doing the work on your machine, not sending the new password to a server to be invented.
If you already use Bitwarden, the generator inside the app is the better button, because the password goes straight into the vault. The website is for a Wi-Fi key, a recovery code, or a machine that should not hold your vault. Generate it, store it, close the tab. A password that only exists in a chat message is not stored.
Use it for one-off secrets. bitwarden.com/password-generator
Bitwarden’s web generator is for a machine that should not hold the vault, such as a shared PC where you need a Wi-Fi password. Generate, move it into the manager on your own device, and do not leave it in a clipboard. If the page ever asks you to log in before it will generate, use the generator inside the app instead. Length beats cute substitutions. Twenty characters, or five random words, and no birthday.