An HSA and an HDHP are two different things.
The HSA is a Health Savings Plan. The HDHP is a High Deductible Health Plan.
More simply put, the HDHP is your health insurance. The HSA is a tax-advantaged plan to help you pay the high deductible for the HDHP with pre-tax dollars.
$2,400 would be more than the minimum for an HDHP is you are in a Self plan, but not quite enough for a Family plan.
But there are other limits - see the IRS Publication 969.
You should ask your HR department if the health insurance that the company signed you up for qualifies as an HDHP (it probably does).
