Wormtear is material that can only be minded in the Capital sectors of the PvP-Area (the top row). Wormtear asteroids appear in one sector at a time. Also, these asteroids appear for a limited time in a given sector, before disappearing.
Any Wormtear mined can be sent back to your station through the outpost in the sector where the asteroids appear ... provided your faction controls that outpost. It takes 5 minutes to transfer a quantity of Wormtear, so make sure your faction controls the outpost until the transfers are finished, or your mining efforts will be lost.