I don't fully understand your concerns. Let me explain what I believe you want to achieve so you can confirm my thoughts.
You want to deploy a Roundcube application to manage your email. This application needs to run in your local machine (Mac OS X?) so you downloaded the OS X VM from here, is this correct? That VM is configured with a dynamic IP but you can set a static IP so it uses the same one all the time.
If you want to use a SSL certificate to access the application, you also need a valid domain (and a static IP). That domain should point to your public IP (and your router will need to forward the requests to the VM's IP).
If you don't want to use a SSL certificate or a domain, you can use the application locally (and don't need to configure a static IP either). In this case, you just need to start the Bitnami VM and access the application with your credentials.
Let us know if this information helps.