Mortar and pestles are wonderful instruments, and aid in making powders, incense, tinctures, and oils. Often enough we run across substances or material that is often tough to handle in its raw form, so being able to grind stuff up into a more manageable form is always encouraged.
For ideas of what you might create using your new mortar & pestle, I've rounded up this nifty website:
As for dealing with seeds and other awkward or hardened substances, try laying out wax paper folded in half, with the substance tucked in the fold. Using a hammer or mallet, crush the material, then dump into your mortar and continue to grind into a powder or whatever courseness you desire.