The Buddha (also known as Siddhartha Gautama, or as Shakyamuni Buddha) is a historic individual who attained enlightenment and taught the path out of suffering. Taking refuge in the Buddha is to trust in the Buddha like our physician, to acknowledge that awakening is possible, and to culivate qualities to become more like the Buddha.
The Dharma refers to the Buddha's teachings, like the aforementioned Four Noble Truths and Noble Eightfold Path. Also teachings like non-self and impermanence, which we will get to at a later time. To continue our earlier analogy, this is the medicine our physician has provided.
The Sangha is the community of Buddhist practitioners. Some define the Sangha solely as monastics (monks and nuns, etc.) But I subscribe to the view of the Sangha as all practitioners, both lay-followers and monastics. The Sangha functions as our nurses, or other patients supporting us on the path to recovery.
These are the Three Jewels, or the Triple Gem, that most Buddhists would say one must embrace to be properly considered a "Buddhist." There are formal refuge-taking ceremonies, but what is primarily important is taking refuge in the Three Jewels within one's heart and mind. Return Home