Structuralism was a school of thought that sought to identify the components (structure) of the mind -- the mind was considered the key element to psychology at this point. Structuralists believed that the way to learn about the brain and its functions was to break the mind down into its most basic elements. They believed, the whole is equal to the sum of the parts.
Wilhelm Wundt, who is considered the pioneer Structuralist, set up the very first psychological laboratory in 1879. Following Wundt was Titchner who popularized the field (he was one of Wundt's students). TItchner was interested in the conscious mind. He used a technique called introspection to try to understand the conscious mind. Introspection is a process of having a person "look inward", focus on, and try to understand the emotion or thought they are experiencing at that moment.
The Structuralism school of thought has influenced psychology in its pursuit of the analysis of the adult mind (the evaluation of the sum total of lifetime experiences). It seeks to evaluate these experiences in terms of the simplest definable components and then attempts to find how these components fit together to form more complex experiences. Another goal is to find how these experiences correlate to physical events. This is accomplished through practices such as introspection, self-reports (of sensations), viewpoints, feelings, and emotions.