Everytime you farm a farming village you get as many "Hops" as you get of resources.
You have a maximum capacity of 2000 hops.
The clue wiith Oktoberfest is to make beer, but to make the beer you also need "Amphoras", this is the easy part, they're floating around in the ocean, just scroll around and you'll find many in a few minutes. The maximum capacity for "Amphoras" are 15.
When you have "Hops" and "Amphoras", you can make beer.
You can get 10 glasses of beer for 100 hops and 1 "Amphora", you will have to wait 5 minutes for the beer to be made.
You can get 25 glasses of beer for 400 hops and 2 "Amphora", you will have to wait 20 minutes for the beer to be made.
You can get 55 glasses of beer for 750 hops and 4 "Amphora", you will have to wait 60 minutes for the beer to be made.
You can get 85 glasses of beer for 1500 hops and 6 "Amphora", you will have to wait 120 minutes for the beer to be made.
Of course, the best is to be active and make beer every 5th minute, but then you need to do the same with your farming villages.
When you've made your beer, you can change it for spells, resources or gold.