You have three "boosted" goods for your city, one at each of the three goods tiers. Tier 1 is Planks, Marble, and Steel; Tier 2 is Crystal, Scrolls, and Silk; Tier 3 is Magic Dust, Elixir, and Gems. You can tell which boosts your city has by looking at the map - the province above your city, the one to the lower left, and the one to the lower right will have a good from each Tier that is your "boost". You can also click your Main Hall and check the Relics tab; the three boosts should be listed along the bottom along with the percentage of boost you have earned.
To increase boosts, you need a combination of tech tree Research and a collection of Relics for that type of boost. Check the Wiki for more detailed information, but hope this helps to get started!