Goods are needed for Guild Expedition (cost is per player per age basis) and Guild VS Guild (cost is based on number of tiles of that age currently held)
Yes you as a player don't get to use those goods personally, but they do provide a lot in return as the things they're used for increase the guild level and that provides FPs, reduced production time for troops, reduced cost of buildings etc
The most effective way of gathering the goods necessary is with treasury GBs. The observatory is a good idea for a new player once you've got the Blue Prints because it only needs Bronze Age goods. Another good treasury GB is the Arc as that one also benefits the individual. Only thing is the Arc being a Future age GB needs Future age goods so you'd need to get the goods from another player if you want to build that