Herbs are plants, and contain many compounds, so unlike most pharmaceutical medications, they often do not have as dramatic an action, but they also usually don’t have as many negative side effects.  As humans, we have co-evolved with plant life for thousands of years.  Our bodies recognize and respond to plants because of this and so can use them for our benefit because of historical use and knowledge gained from modern research, if we so choose.
In herbal literature and in my personal use of herbs, I have found that herbs can act to strengthen and balance the body.  They can act as anti-inflammatory agents, have antioxidant effects, and are able to protect, support, and balance organ systems, such as the liver, heart, and adrenal glands.  In this way, they can actually work with the body to restore or increase health, which is where the body naturally wants to be.
In my shop, I would say my customers come from 3 camps: (1) those that already prefer a more natural approach to managing their symptoms, and/or would like to do more to address the “root cause” than treat symptoms; (2) those that are currently on medications and would like to get off of them because they are concerned about the long-term implications or because they do not like the negative effects of the drug; (3) those that are not really being helped by anything and are willing to try something like herbal medicine that they may be quite skeptical about.
The most common things people come in for, and the most common complaints herbs are often able to help with, are nervous system imbalances, like anxiety and insomnia;  digestive problems, such as acid reflux, irritable bowel complaints, indigestion; stress-related imbalances, such as adrenal fatigue and low immunity; cardiovascular problems, like high blood pressure and cholesterol, sluggish circulation; and much more!  It is very gratifying to be able to help someone feel better because of my knowledge of how herbs can help and their willingness to take them and give them a chance to work.