WAIT!
Don't flood the box! Flooding is the right thing to do after every flush to get a better next flush. Your box isn't ready for that yet!
When you received the box, it might not even be totally incubated - then you have to let the mycelium incubate first. Simply put, all the contents have to be covered with fluffy white stuff - if there are big areas not covered in white, fluffy stuff (the mycelium) then it needs to incubate a little longer before you can grow mushrooms!
To incubate the mycelium, put it in a dark, dry place with temperatures between 25 and 26°C. A little less is fine, but takes longer. It must not be over 27°C or you might kill the mycelium!
When all of the box is covered in white, fluffy mycelium, you need to fruit the mycelium cake. You might want to put it in the fridge at 5-8°C for a few hours, this usually helps fruiting, but it's not totally necessary.
In my opinion it's easier to use a bucket than the plastic bags: Just open the myceliumbox and put it in a bucket. Put some water inside the bucket (one centimeter or so) and cover it with clear foil. Put this bucket in a warm room (anything above 20°C is totally fine) where it gets some light, but not direct sun light. The shrooms just need a little light to know they have to grow, and to know where up and down is. They are not plants and don't need light for energy.
Now check at least once a day if the inside of the bucket is still moist, and open the foil once a day and fan a little fresh air into the bucket (mushrooms consume oxygen, just like we do).
If you need a few pictures to get it better, look here:
http://www.fungifun.org/English/Pftek#a5
this is the pf-tek method for growing mushrooms - as you have a ready-made grow box, you don't need the steps before that, but from the point of incubation, it is almost 100% the same (only the pf-tek cakes are put into a bucket without a plastic box - but that's just a minor difference).
