To harvest the plant you can right-click it. Left-clicking will harvest the plant as well as destroy it, leaving only crop sticks. Harvesting Coffee may yield Coffee Beans. Left-click harvesting can also produce Coffee Seed Bags.
Coffee Beans are used in brewing Coffee and Dark Coffee, both which give you the speed and haste buffs. Coffee Beans must be Macerated or crafted into grounds to be used in brewing. When right-clicking an empty Crop with a Coffee Bean in hand, it plants the bean which eventually grows into a coffee plant with a GGR of 1-1-1.
Note: Since Aurelia and Ferru look identical to Coffee prior to the final stages of growth, it is advised to place Iron Ore and Gold Ore under the farmland instead of 4 dirt blocks to ensure maturity of the plant. Having both works so long as they are within 3 blocks.
When growing Coffee, an extreme amount of patience is needed. It is highly recommended to use a Crop-Matron filled with Weed-EX, Hydration Cells, and Fertilizer. It is important to note that excessive use of Weed-Ex will lower the crop's stats over time.