How can I effectively seal plywood for outdoor use?

To effectively seal plywood for outdoor use, you can apply a waterproof sealant or outdoor wood sealant. Make sure to sand the plywood first to create a smooth surface, then apply the sealant evenly using a brush or roller. Allow the sealant to dry completely before exposing the plywood to outdoor elements. Repeat the sealing process every 1-2 years to maintain protection.