Mines and Mills are very useful.It gives us more resoures over a long period of time but in order to make these buildings work you need to put villagers inside of the mill/mine.
When starting out you'l need to have friends or allies due to the fact all level one mills and mines require to recruit an ally to do a job then you can procede to place peasents into the mill or mine and begin your resource farming.
Lumber Mill: Produces wood only requires peasents after level 1 mill. Chopping down trees is faster and gives you items for collections however using the Mill and selecting the 8 hour option is useful while playing and offlien so when you come back youl usualy never be low on wood.
Stone Mine: You can use a Stone Mine or stone Veins but unlike the lmber mill it is a lot faster to use the mine over the natural resources due to the fact stone veins are not very abundant and take a good couple of hours to be re-usuable unlike trees which are the most common resource to spawn.
Farms and Mills: These both produces food and has diffrent variations for example some require your friends help to build then require you to put peasents while others just require you to put peasents into it.Farms take up 1 peasent and cost wood to buy and mantain and is a quick way to obtain food quickly.
Gold Mine: Produces gold and is the simpliest and is the most effective way to obtain gold excluding invading empires and doing island quests.Gold is one of the eaisest reources to obtain due to the fact you cant get by doing most actions which complete tasks which give you about 100-200 gold a piece.