Go to Morroc
Talk to Aberk Ugarte (Equipment Socketing NPC).
The NPC will ask you to bring 11 items. 1 item will be converted to  slot and others will be consumed by the NPC
1x Shoes  (will become slotted).
10x Shoes  (will be consumed by the NPC).
100,000 – 150,000 zeny (Depends on the items but mostly that is the range).
Product = 1x Shoes