A piece of wood that lays on the ground for 24 hours or more is wet,and will smoke when burned. For a smokeless fire,and an easy starting one,use only dead branches broken from the tree.
If you hold a piece of wood against your lower lip,and it feels cold,it's wet wood.
Wood is made up of a bunch of air cells,like a sponge,surrounded by celulose. If yo pick up a handful of soda straws and look at the bunch from the end,that's what wood looks like under a magnifier. The holes are the air cells,and will readily fill up with moisture,just like a sponge.

