The Coaches and Press rankings are determined by looking at the talent on each team along with the performance of each team on the field. The talent component decreases as the season goes along. Each ranking factors in each component slightly differently which creates the slight differences between the two polls.
The WIS rankings use the Coaches and Press rankings as a starting point and then modifies each team's ranking based upon home record, road record, neutral record, scoring margins, and strength of schedule.