The code is literally A, T, C, and G, which is stated to be an acronym for the four types of Codes found in a DNA molecule. A gene is a specific section that gets read in groups of three, each telling the cell which amino acid to add to build a protein. Those proteins shape your brain, how neurons connect, how much dopamine or serotonin you release, etc. In terms of dictating your behaviors, it’s usually a combination of many genes working together. Each gene usually has a small effect, some more than others of course, and that effect often depends on the environment. Together, they influence the release of certain chemicals in your brain depending on the situation, which as a byproduct can influence your behaviors.