Each guide goes from no account to keys pasted into SimDrive: creating the account, making a bucket, generating a key that works, and what to type where. Pick your provider — or, if you have not chosen one, see what each costs first.
The secret is shown once. Every provider shows the secret half of a key when it is created and never again. Copy it into SimDrive straight away; if it is lost, make a new key rather than looking for the old one.
A key limited to one bucket cannot list buckets. That is the safer kind of key and SimDrive is built for it: it asks you to type the bucket name instead of offering a list. It is not an error.