Wandering trader farming is the process of farming wandering traders for their trades, and then disposing them and their llamas to get leads and leather. It can be a very good farm to built since it is the only glitchless way to renewably farm items like sand, red sand and small dripleaf, however it will require several emeralds, so you might want to hook it up to a villager trading hall or raid farm.
There will need to be a platform over an ocean with lighting. There will need to be a bell in the middle, a hole around the bell with trapdoors to trick wandering traders into walking over it and a water stream in that hole which will transport the trader to the player. There will also need to be a system which will activate and deactivate a dispenser which will dispense lava to the trader after the player is done trading (using a lever is best), and also signs and a collection system so that the leads and leather won't be burnt.