To put a chain on a lawn mower, you need a wrench and pliers. Put the lawn mower on a level ground to locate the screws and the nut bolts as you check the manual. Seat the chain on the sprocket seat and pull the ends of the chain to position it. Place the master link and secure it with a clip to position the opposite pin. You can get the procedure on http://www.ehow.com/how_8729642_put-chain-lawn-mower.html.