There is an article on how to get started here:
In a nutshell, if you already told IPS what domain you wanted to use during signup, all you need to do is CNAME your website to the address they gave you in your welcome email. If you did not pick your domain yet, you'll need to open a support ticket and let them know what name you want to use. They'll set it up on their end so that you can then later CNAME the domain to IPS.
Your welcome email should have the temporary URL and username/password you can use to get started customizing your community while the DNS stuff is worked out. If you did not get that, I would create a support ticket in the client area so they can resend it to you.
Also... some general guidance on getting started once you can login can be found at:
If you have questions along the way, feel free to ask. We're a friendly bunch here. 🙂