Yes, this is true. Native Indian Americans were used as slaves and when this practice was frowned on in Britain, Africans took their place, shipped in, mostly but not exclusively from Western Africa. However, native Indian americans used slavery before any Europeans arrived in America.
It was quite common for one tribe to keep captives for ritual sacrifices, as well as for slave labour on the unpopular work. It was different in that captives might gradually be allowed to live freely on the fringe of the tribe, and some were adopted when the spiritual time was deemed to be right.