Use the “passwords” feature to check if one of yours is compromised. If it shows up, never ever reuse those credentials. They’ll be baked into thousands of botnets etc. and be forevermore part of automated break-in attempts until one randomly succeeds.
More details about the k-anonimity process. https://blog.cloudflare.com/validating-leaked-passwords-with-k-anonymity/
The short answer is that they download a partial list of passwords that hash to values starting with the same 5 characters as yours and then check if your password hash is in that list locally. This gives the server very little information about your password if it was not breached and more if it was (but then you should change it anyway), making an elegant compromise