I gave a brief intro on KRACH in one of my first FanPosts so I thought I would repost for those of you who missed it.
There are 59 teams in college hockey. The pairwise is an approximation of the selection process for the NCAA tournament. Again, College Hockey News does a great job explaining the process. The top 16 teams are selected for the tourney. Conference tournament champions get auto-bids so teams rated near 16 can be displaced if a lower ranked team wins it's conference tournament.
Teams are compared pairwise against every other team in the country. The comparison criteria are RPI, common opponents, and head to head. If teams tie in a comparison, the team with the higher RPI has genereally wins the overall comparison but it is not an official rule.
Please read those FAQs before asking further questions as they likely have your answer.