You roll 4 6-sided dice.<br/>A 1 or a 2 is a -1<br/>A 3 or a 4 is a 0<br/>A 5 or a 6 is a +1<br/><br/>So, if I get 2, 4, 5 and 6, that's a -1, 0, +1, +1. Added together, that gives a +1<br/><br/>I compare that to my skill rank that was being tested, and move it up by 1. That's the final result.