The most fundamental unit of the Industry Set is the "Ore (Tier 1 Industry Item)".
You can get any Tier 1 items (not just for Industry Set) by playing the game (match 4+ items in any of settlements, or open treasure chests) or by buying them from the in-game store. Once you're further along in the Capital City, your higher tier buildings (such as "Barrel") will also generate Tier 1 items (such as "Ore").
When you combine three (or more) ores, you receive a "Barrel (Tier 2 Industry Item)":
Combining three (or more) barrels will result in creating a "Shed (Tier 3 Industry Item)":
Combining three (or more) sheds will create a next tier building - a "Warehouse", and so on.
Here is the progression list of buildings in the Industry Set:
The rewards you receive from each set are based on the highest building you have completed (so if you have Ores, Barrels and a Warehouse, your rewards will be calculated based on the Warehouse because it's the highest level building), and they scale up accordingly.
Industry Set will produce coins for you... and if you create higher level buildings in the set, you have a chance for additional turns!