Asking for information about genetic influences on behavior is asking what appears to be a simple question about a huge topic that is far from completely understood. As a result, there is no one simple answer that summarizes how genes influence behavior.
We do know that some medical conditions have a genetic component. There is a "genetic predisposition" to alcoholism, for example, and there are types of behaviors that are frequently associated with people who suffer with alcoholism. So the genetics that make one person more likely to be sensitive to the effects of alcohol will influence that person's actions in some way - possibly causing that person to make a conscious decision to abstain from alcohol, possibly causing that person to become an alcoholic. Other genetically based conditions influence other kinds of behaviors in varied ways.