Using Serveo to create custom domain name

http://serveo.net/#manual

I am attempting to add my own domain name with serveo but I am stuck on this one part of the process because it is unclear to me. It says I need to add two DNS records for the domain or subdomain I want to use but the problem is I don't know where to add these records. Furthermore I don't know how to do what it states to do with them. How do I go about doing this?