And how big is it, and will you be filling it to capacity or leaving spaces? Does it have a fan or is it a still-air one? Did it come with instructions?
Run it dry initially until you establish what you need based on answers to Foxy and Marigold's questions. If the air in the environment is damp enpough you won't need any water until hatching. If it is very dry you will need to add a little, but how you do that in whatever machine you have I don't know?