According to Samsung's web site:
Self Clean (also called Pure Cycle or Self Clean+) is a special cycle that prevents mold. It's designed to clean areas of the tub where moisture and detergent residue may accumulate. A normal cycle may not be able to reach these areas. It takes approximately one hour to run Self Clean on a top load washer and four hours to run Self Clean on a front load washer. After the Self Clean begins, the estimated remaining time will display.
To run a Self Clean cycle, make sure the washer is empty, press Self Clean, and then press Start. If residue or suds appear during a Self Clean cycle, we recommend running another Self Clean cycle afterwards.
The Self Clean reminder LED will display after 20 washes on a top load model or 40 washes on a front load model. Although you do not need to run a Self Clean cycle immediately, we recommend that you run one at your earliest opportunity. It's also a good idea to run one at least once a month if you do not do many washes in a month