Repairs: Filler, Putty, Patches, etc.

Use a tool called a plug cutter to make face-grain plugs that match the area to be repaired--or to cover screw holes. Glue and hammer the plugs in place, then saw and sand them flush after the glue dries. 

To make a Dutchman repair, cut out a patch of the desired size and shape, carefully knife its outline over the damaged area, use a chisel to chop out a pocket, glue the patch in place, and sand it level after the glue dries. Some designers, like Siosi, make this a signature look.

Depending on the gap that needs repair, you can use a chisel to make a wedge, splinter, strip, or any desired shape to glue into a void. Allow the glue to dry, then saw and sand flush. 

If the wood fibers have only been compressed but not torn, judicious application of steam can sometimes cause them to swell back to their original position. Soak a 100% cotton rag in water, then use a regular household iron to thoroughly heat the area. Allow the wood to dry completely, then sand to level as needed. 

This trendy method is a good way to fill knotholes so they don't collect dirt and grime. Fill the knothole slightly above level, allow to cure, then scrape and sand level. Epoxy can be tinted to different colors as desired. 

Burn-in sticks are solid bars of material (often shellac or a similar resin) that come in various colors to match different wood finishes. They are designed to be melted and used as a filler for imperfections in wood--usually after stain and finish are applied.