Share passwords across my Apple devices

The majority of passwords associated with your Apple ID are stored within keychain encrypted and synchronised over the air between all devices logged into the same Apple ID automatically.

You need do nothing else .

You basically have three options:

1. As Keith Doherty3 has pointed out, they would be stored in your Apple Keychain. If you use the same Apple ID on each of your devices AND have this keychain synced to your iCloud account, then you should have all of your passwords (stored in the keychain) available on all of your devices.
2. Use a 3rd-party password manager. A very popular one is 1Password. FWIW, I have been using 1Password for quite a few years now, and it has made my computing life far simpler.
3. Write them down on a piece of paper. This one is not really recommended, unless you have a means to store it securely ... but, in some cases, where the first two fail you, it could be your only resort.