Slavery was very common in Golden Age Athens. This was true to such an extent that it is believed that only the very poor in Athens did not own at least one slave. Even peasants typically owned a slave or two.
Slaves were typically (unless they were unlucky enough to work in the mines) treated as members of the family in which they lived. They were still slaves, but could be freed if they could save up enough money. In terms of work, slaves were typically just doing the same sorts of things that their owners were doing. They were help for the owners, not a separate laboring class.
So, with regard to the relationship between free people and slaves, the free people clearly had the upper hand. They owned the slaves and had a great deal of control over them (though they were legally forbidden to kill them). On the other hand, there was not the same sort of distance between slave and master as in the American South, for example. The relationship was on much more of an equal level as slave and master did the same kind of work together.