yep, you need 1 coal, 8 soulsand, 8 glowstone and 1 diamond, plus one soul forge and a furnace.
1/ cook your 8 soulsand into your furnace (using the 1 coal or something else).
2/ mix the result with glowstone
3/ put 1 diamond in the top slot of the sould forge and the 8 from 2/ in the fuel slot.
4/ after a good wait, you have 3 new soul shards, enjoy.