Similar to day care for kids. They are fed, get help if needed going to the bathroom, field trips, and visits from people who talk on subjects that may be of interest to them. They also may have movie time, tv time, and medical people may come to do wellness checks (heart, blood pressure, etc). in short it is a place to get out of the house/NH/AL and interact with others.
It's a day for adults to show our devotion towards them. A lot of adults are struggling with their lives because of the disabilities. So we help them at this day to encourage them towards their fights with lives.