An HSA is an account that is setup by individuals, but if employed, often times are offered via their employer. It is important to understand that the account belongs to the individual, NOT the employer. The HSA is a triple tax-advantaged savings vehicle where the funds can be used for qualified medical expenses. You contribute money on a pre-tax basis, your money can be invested or earn interest (no taxes on such growth), and be withdrawn at any time and with no penalty so long as the money is used for qualified medical expenses. You can think of the HSA as the 401(k) for your healthcare with a bit more flexibility. Typically, people can go to one of several providers to open up an HSA account. They will be provided an account where they can view their balances, request reimbursement for funds paid out-of-pocket, manage their account, and receive a debit card to make qualified medical purchases.
The individual contributions limit for an HSA is: $3,450 (2018) / $3,500 (2019).
The family contribution limit for an HSA is: $6,900 (2018) / $7,000 (2019).
In addition to the limits above, if you are 55+, the catch-up contribution is $1,000.
Source: Rev. Proc. 2018-27: Changes to HSA contribution limitation for 2018
Source: Rev. Proc. 2018-30: HSA contribution limitation for 2019