Do I have to get an HSA if I am on a High Deductible Health Plan?

No, not at all, but you should consider getting one. You will be able to make contributions into your HSA and pay for qualified medical expenses using your pre-tax dollars! Why waste money if you don’t have to? Even if you don’t have the money to put into an account today, you can open an account and “establish” it by funding it with as little as $0.01. The moment you do that, all qualified medical expenses become eligible to be reimbursed out of your HSA whenever you do have funds to put into it.

Source: "Publication 969 (2018), Health Savings Accounts and Other Tax-Favored Health Plans.”