Here is the link to these excerpts giving more details;

About HSA’s

• A Health Savings Account (HSA) can help patients with high-deductible health insurance plans cover their out-of-pocket costs.
• Contributions to HSAs generally aren’t subject to federal income tax, and the earnings in the account grow tax-free.
• Unspent money in an HSA rolls over at the end of the year so it’s available for future health expenses.
• High-deductible health plans, which are a requirement for HSAs, aren’t always the best option for patients, especially those who expect to have significant healthcare expenses in the future. Those patients may be better off with an insurance plan that charges higher premiums upfront but covers a greater percentage of their costs.

Others Can Contribute. Contributions can come from you, your employer, a relative or anyone else who wants to add to your HSA. The Internal Revenue Service does, however, set limits. For 2019, for example, the limit is $3,500 for individuals and $7,000 for families, plus an additional $1,000 “catch-up” contribution for anyone aged 55 or older by the end of the tax year.

Pre-Tax Contributions. Contributions are typically made with pre-tax dollars, through payroll deductions at your employer. As a result, they are not included in your gross income and are not subject to federal income taxes. In most states, contributions are not subject to state income taxes.