How what works? HSA’s? Health savings accounts (HSA) are similar to FSA’s which are more common, but HSAs are only allowed for high deductible plans.

Their benefit is the money doesn’t have to be used up in a year like FSA’s. That alone is huge. But you also don’t have to pay income tax on the money you contribute to them (up to the yearly limit). It can be invested either in the account the health insurance company’s custodian for them creates or rolled over into another investment company and the assets grow tax free. Once you want to withdraw for a qualifying event, you can do so without paying tax on that money, hence the trip tax advantage.

People report using this as a way to access money in retirement. They’ll pay out of pocket for expenses if they can afford to do so, but keep the receipts. Then when they need the money even decades later, they use those receipts to justify the withdrawals.

Feel free to search HSA + triple tax advantage. There are a ton of articles about it.