Wessmarine, much depends on the wood, it's location, use and finish. Generally, you need to remove any and all damaged portions. No, there isn't a magic goo in a ca that can restore rotten wood into a serviceable material again. You can embalm the rot with a plastic coating and fillers, but the weakened wood remains.
For small repairs, drill out the area with a flat bottomed bit. Cut a plug of similar dimension and glue it into place. When cured, chisel off the excess and sand flush. If the hole is fastener size, then just fill it with putty and sand flush. As a rule, replace wood with wood if the damage is large enough to threaten the integrity of the piece. If the repair area isn't large enough to weaken the piece significantly, then a filler will do.
The have been countless previous threads here about wood repairs. Use the search tool thingie and absorb some repair techniques.