This is the simplest and quickest of the steps required to set up your humidor.

Take a clean cloth or unscented sponge and wet it with some distilled water.  Now, wipe down the inside of your humidor so that it's nice and wet.  The idea here is to leave a layer of moisture on the wood, not soak it.  What you're trying to do help the wood absorb moisture more quickly.  However, if you use too much water the wood can become warped and throw off the seal, which is a big no-no!

Once you've done this, fill a small glass (shot glasses work well) with distilled water and place it inside your humidor.

Move on to the next step which is to charge your humidifier.