Hi Steve,
You are never required to contribute to your HSA, it is essentially an account created entirely for tax advantages. If you contribute to an HSA through your employer, then the contributions are not taxable. You can read more here: https://blog.turbotax.intuit.com/tax-tips/basics-of-health-savings-accounts-83/.
You can contribute outside of your job. There are no limits on your adjusted gross income for a contribution, but there are limits on how much you can contribute.
I hope this answers your question.
Take care,
Jesse W.
