If you’re referring to a Windows Azure Storage account, the storage account name would be the dns prefix you created (e.g. mystorage.blob.core.windows.net – the name would be mystorage).
You then get two keys – primary and secondary. Specify either. You have two so you can give one out to someone (such as giving the secondary key to a 3rd-party monitoring company) and revoke it by changing the key, without impacting you (assuming you’re using the primary key for yourself).