Go to youtube video link here: https://www.youtube.com/watch?feature=player_embedded&v=dUAWxdch9ak
Or follow steps below
Go to pinion and ring gear in the Solidworks model..
Rotate and position pinion gear to mesh with ring gear.
Open up "mates" in SW then "mechanical mates" then click on "gear" for this case.
Click on mate selection in the feature manager, then click on a cylindrical surface of the pinion gear.
Click on the cylindrical surface of ring gear .
In this case the pinion has 10 teeth, so under "ratio" the first entry will 10. Then the second entry will be 80. This is because the pinion has 10 teeth and the ring gear has 80 teeth. Lastly, click in check box "Reverse". Then click OK twice. DONE!