今天问了才知道是employer给存的health reimbursement account，怎么用还不清楚。

See, that's what I mean. :-)
To use this is simple:
1) ask if this is pretax money or not. I guess it should be pre-tax, which means this part of money you do not pay any tax. (I only guess because they have too many different names for this kind of account).
2) then it can only be used for medical related expense. for example, see doctor co-pay, medicine co-pay, etc. Different plan may differ. Ask your hr.
3) your account should come with either some checks or a debit card, pay with them.
4) say that you spend 1000$ this year. At end of year tax time, they may send you a bill saying that this 1000$ is your income. Do not be surprised, when you prepare your tax return, check to make sure put it as qualified medical expense, then you do not need to pay tax on them.


It is that simple.