Hi, thanks for your question. The "ratings" you are referring to are called "Community Ranks" and they reflect the participation in this community. So if you visit regularly and just read you will be ranking up in the "Visitor" ranking, when you post messages you will become a Contributor, if you keep tagging messages you will rank up in the "Collector" rank and if others find your messages useful you will advance in the "Advisor" category.
Basically the rank gives other users a quick guideline about the type of user he is having conversation with on the forum.
The highest level are our "Super Users" - they are highly knowledgeable Skype users that are experts on their field and know how to share their knowledge by creating good answers.