Individuals are largely unable to have much effect on the social structure of a society. It is only in extreme cases that any one person's actions can change such a structure. However, the combined actions of many individuals can matter. Therefore, the role of the individual is somewhat ambiguous. Individuals can matter, but only (except in very rare cases) if they are part of larger groups.
Social structures are much larger than any one person. Social structures are made up of the shared norms and values and understandings that most of us have in a given society. No one person can typically do much to change that. However, large numbers of individuals, working together, can change social structures.
Let us think about the Civil Rights Movement of the 1950s and 1960s. There, one person, Martin Luther King, Jr., can be said to have had an impact on social structures. He did a great deal to remove the idea of white superiority from our shared norms and values. However, the movement also showed the importance of large numbers of people working together. King had an impact, but the actions of the thousands of individuals who made up the movement (and the millions who responded to it) were what really changed our social structure.
So, the role of individuals in a social structure is complex. They are generally not able to act to change it on their own, but they can help to change it as part of a large group.