IF the furniture is unfinished - a whitewash is simply a white semi-transparent stain.
You can make one yourself by thinning an oil-based paint with thinner until you get the desired opacity.
Apply the mixture with a rag until you achieve the effect you are looking for.
Finish with an acrylic polyurethane - it will give you a clear finish. An alkyd poly will yellow the finish - likely spoiling the white colour.
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