How did the Enlightenment answer the question of what it means to be human, and what it means to live a life of meaning and purpose?

For a thorough exploration of this question, it might be helpful to consult the two-volume work, The Enlightenment by the late historian Peter Gay.
Gay's thesis hinges on the notion that the Enlightenment marked the "rise of Modern Paganism." He is explicit in saying that he is not using the term to refer to the sensuality of its proponents, notably Rousseau and Hume. Rather, he is referring to the era's adherence to Classical modes of thought and living (Gay 9). 
The typical philosophe was "a cultivated man, a respectable scholar, and a scientific amateur" (Gay 14). In both their lives and in their writings, Enlightenment thinkers adopted the view that individual freedom, which sometimes meant abandoning one's country for a freer one—as Voltaire did when leaving France for England—was of the utmost importance. They did not marry, but kept what were then considered "mistresses." 
Living according to one's desire and being committed to the free expression of one's ideas were the highest purposes. This predictably meant that a thinker had to be as distant from the Church as possible. It also meant that one should be committed to cosmopolitanism, which involved engaging with as many different ideas and people as possible. The salons, or drawing rooms, of wealthy patrons and royals provided many opportunities to mingle with and exchange ideas with luminaries from around the Western world.