As a first step, you will have to sand the work piece and remove any previous finish. The varnish comes either as a spray or can be applied with a brush or a foam applicator. You can thin the varnish, if necessary. You should follow the grain and allow the coat to dry for at least 24 hours. Apply another coat after sanding, let it dry and repeat these steps until you get the desired result. The drying time of varnishes varies significantly. It can be as short as 1 day up to a couple of weeks, depending on the composition of the product. Check the producer’s recommendation and the timeline for your project before buying the varnish.Varnish finishes are usually a bit “heavier” and thicker, so you might only need 1 to 3 coats to get a perfect finish. Varnish finishes are a bit rougher than the shellac finish. If they are applied correctly, they are not brittle though. You can find more details on Wikihow.