There's nowhere to "login" to Let's Encrypt regarding renewals. Your ACME client (which could be embedded into some kind of control panel or other software) is responsible for acquiring/renewing your certificates. You do have an ACME account tied to a private encryption key that was created when you first acquired your certificate(s). Your ACME account can have one or more email addresses on file where you will receive expiration warning notices. There is nowhere to "login" to your ACME account. It is simply accessed via the ACME API by your ACME client using your ACME account private encryption key.
It's a certificate transparency (CT) log aggregator. Since a certificate contains absolutely no confidential information, being able to confirm its details only aids with security.