We invest a lump sum of our money into the S&P 500 on your behalf. You pay us a monthly membership fee, and that entitles you to the earnings that investment makes over time. You start with a larger position and get the benefits of compounding returns sooner, without having to save up and invest that lump sum yourself.
When you decide to leave, the asset is sold. Our original investment is returned to us, and all the earnings are yours to keep.
Example: We invest $5,000 for you. You pay us $30/month. The asset grows over time. When you move on, we reclaim our $5,000 and all the earnings above that are yours to keep.
The longer this money has time to work in the market, the greater those earnings will be.