Clean the surface that needs repaired. Use wood cleaner and a damp cloth to clean the gash. Depending on how long the gash has existed, discoloration might occur. This is nothing to worry about, just ensure that the dirt is removed from the gash.
Apply wood putty to the gash: Scoop wood putty onto the putty knife and fill the gash with the putty. Overfill the gash, letting some putty overflow. Allow the putty to dry. This usually takes several hours. Consult the putty packaging instructions for drying time; you don't want to move to the next step before the putty is dry deep into the gash.
Don protective glasses and sand the putty with sandpaper. Use a coarse sandpaper, and sand with the wood grain. Once the putty is almost flush with the table surface, switch to a fine-grain sandpaper to smooth the putty.
Wipe the sanded area with a damp cloth to remove dust from sanding.
Apply wood stain to the repaired gash. If needed, apply a sealant once the stain is dry.