Code:
X:=Self.X()
Y:=Self.Y()
Z:=Self.Z()
weapon:=Self.Inventory.LeftHand()
Map.UseOn(!weapon!, SPIDER_WEB_ID, !X!, !Y!, !Z!, 2)
u must have a weapon in left hand(<--). Don't forget change SPIDER_WEB_ID.
If I helped u, please rep me. Good Luck!