It is important to keep the air circulating to allow the rotting process plenty of oxygen. If your bin gets stinky the food is not getting enough air as it decomposes. Frequent stirring will prevent this. You may need to add moisture from time to time in addition to the food. Never let the bedding dry out.
Water is fine.
Fruit juice or water from cooking veggies is even better. If the bin is too dry, the food will stop rotting and the worms will not be able to eat it. The process is very slow. You won't see much change from day to day. Rugged plastic vermicomposter with easy to assemble ventilation tubes and vents.