Rolls is an attempt to caputer the fact that the result of a roll can be more complex than just pass/fail. Rolls offers a way for the DM to generate “multi-outcome DCs”. A multi-outcome DC is a set of roll ranges paired with outcomes. For example:
|8 and up||Pass|
|5 to 7||Mixed Result|
|12 and up||Critical Pass|
The ranges are used to determine the outcome, for example if the rolls an 8 they pass the check, on a 6 the result is mixed. The ranges and results in the public section are read to player before he rolls (or plays a card). The results in the private section override the public result if a player happens roll in there range, they tend to be a pleasant (or unpleasant surprises). For example if the player rolls a 13 they the outcome is Critical Pass not Pass since private results overrule public results.