In order to use the trap material, you have to buy one of the various convert trap skills. The wording of this skill is a bit wierd, since you aren't converting a trap, you're creating a trap out of the trap material. I experimented with this skill a bit, but found it wasn't really my style, so I don't really know which traps would be best to use, but I believe the Scorpion trap is a popular one.
