Samoa, formerly called "Western Samoa" is an independent country, made up of two main islands (Upolu/Savaii), and several smaller islands. For currency, they use the Samoan Tala, and share the same day with New Zealand & Australia (1 day ahead of USA). They also drive on the left side of the road.
American Samoa, consists of one main island (Tutuila) and several smaller islands (Manu'a) to the east. It is a US territory. They use the US dollar, and share the same day with Hawaii/USA. They drive on the right side of the road.
Both share the same language and traditions, though modern-day culture may differ.
A few years ago, Samoa used to drive on the right side of the road, and had a closer time with American Samoa. However, due to financial and political interests, they changed it; which, for American visitors, can mess them up. A flight from American Samoa to Samoa is less than 30 minutes; but once you cross over, you switch driving lanes, and gain/lose an entire day.