How do I apply top coat?

How you apply top coat depends on surface, but general steps are similar. For interior and exterior house walls, after primer or undercoat has dried, lightly sand with 220 grit sandpaper to smooth bumps, wipe dust with tack cloth, stir topcoat paint, not shake, pour into tray, use quality roller and brush, cut in edges with brush, then roll walls in W pattern for even coverage, apply thin even coat, let dry 2 to 4 hours for latex, then apply second coat. Keep temperature 50 to 85 degrees and low humidity. For wood furniture, after stain dried, apply thin coat of polyurethane or varnish with fine brush or foam applicator along grain, let dry, lightly sand with 320 grit, wipe dust, apply second coat. For automotive, after base color flashed 15 to 30 minutes, mix 2K clear coat with hardener, spray with spray gun in even overlapping passes, 2 to 3 coats with flash time between. For nails, after color polish dried 2 minutes, load brush with top coat, apply thin floating stroke from base to tip, cap free edge, avoid pressing hard. So apply top coat in thin even coats, with proper drying and light sanding between coats, in clean moderate conditions.