Adding an Access Key to your existing account will expand your user's access. Access Keys grant you access to Sub-Accounts. Each Access Key is related to a Role which grants you specific permissions on that Account. For example, if you're working with a Client that already has an Account they can create an Access Key for you granting full or limited access. If you're looking to Delegate an Access Key to another user or for API access please close this pop-up and navigate to 'Settings > Access Keys'.

First, you need to click on My account, click on security then click on the received access key.

If someone already has an account in System, then you create the access key and add it here, then this user has access to your account. You can also manage the level of access to this client, this key is similar to roles.