I've created an AWS Organization to try out the project management approach #3 - separation by AWS account. With this approach I shall have clear separation between projects so they don't have access to each other resources.
To observe the resource separation I needed at least one separate account in each of the organizational units, so I've created an account instead of inviting an existing one and assigned it to the necessary organizational unit.
What confused me afterwards is that the account was successful created and I've received two "welcome" emails from amazon, but in none of them was given access information for this newly created account (like usual sign-in link to set the initial password).
Therefore my question: how to sign into this newly created AWS root account?
To access the newly, via AWS Organizations created root account you should request a new password (via "Forgot your password?" link) like it is described here.