2:3 symbol next to the arrow means that you get three pieces of a processed resource from every two pieces of an unprocessed resource; any remaining single piece may be processed at a 1:1 ratio.
X2 symbol next to the arrow means that you get two pieces of a processed resource from one piece of an unprocessed resource.
+1/-1 symbol next to the arrow means that after processing any quantity of the resource you obtain one piece more/ fewer of the processed resource.
No symbol next to the arrow means that the resource is processed at a 1:1 ratio.