Athens was a true democracy for most of its existence, in which all governmental decisions were made by an assembly of citizens. Any male natural born person could become a citizen; women and aliens were excluded. All citizens were expected to attend meetings of the assembly; if one were seen in the Agora (marketplace) while the assembly was meeting, he was normally marked with red dye (applied by two slaves who carried a rope dipped in dye between them.) The dye subjected him to public embarrassment, and also to a fine. Athenian democracy was not stable; over time aristocratic citizens grew more and more powerful while small farmers often lost their land and were forced to sell themselves in to slavery.
Sparta was situate in an area known as Messenae. The Spartans did in fact require the Messenaen people (Helots) to work as agricultural slaves. More importantly, the Messeanaens substantially outnumbered the Spartans, so there was the constant threat of a revolt. It is for this reason that the Spartans were quite militaristic. it is not that they were bellicose by nature; rather it was a matter of survival. They were not "freed" for military service while the Helots dutifully worked the fields; it was the Helots whom the Spartans were required to keep under constant vigilance.
Sparta was ruled by two kings from two rival families. They often disagreed with each other. Their primary role was military leadership in battle. There was also a council composed of twenty eight elders who were responsible for foreign and domestic policy. There was an assembly comprised of all citizens, which in turn elected five Ephors, or overseers who held substantial power.
Sparta did not necessarily depend more on slaves than Athens; the Helots were held in servitude as a means of keeping them subjected rather than a source for servants. Both poleis relied on slavery to a substantial extent.
Women enjoyed more privileges in Sparta than in Athens, although they were not allowed to wear jewelry or other ostentatious displays of wealth. It was considered a privilege to be the wife of a victorious warrior.
The main difference between these poleis has to do with their governmental system. Their respective choices of governmental systems tells us something about what they valued.
The Spartans had a monarchical system that relied heavily on helots who worked the land, freeing the Spartans themselves to train for war as their full time profession. The Spartans choice of such a system tells us that they valued order and conformity as a way to maintain their strength. They felt that they had to be very unified in order to remain strong.
By contrast, the Athenians had a democratic system that was not nearly as dependent on slavery. It gave its people a great deal more leeway to differ from one another and to express those differences. The Athenians were, in this way, much more like modern liberal societies than the Spartans were.