think hunter has it right ^^ (your question implies an issue there....) Can try a combination of operating the gearshift, nudging prop, flywheel by hand (motor off) -- try to free up the gears. If you forgot to add oil, I would first fill it up and see if the mechanism will work for you (shifts in and out of gear -- again, may have to nudge prop or flywheel to shift.) If seems to operate normally, can try motor. Can't hurt to be optimistic.