The 1095-C is the form received by taxpayers that shows insurance coverage by a medium to large employer. You do not need this for your tax return.
The 1099-SA is the form that shows distributions from your HSA (i.e., money you spent out of the HSA on qualified medical expenses). If you didn't spend any money out of your HSA in 2018, you should not have received a 1099-SA (in this case, don't worry).
If you did spend money out of the HSA in 2018 and you did not receive the 1099-SA, then contact the HSA custodian and ask for a copy (indeed, it may be available online at the custodian's website). The HSA custodian is the financial institution that issued the debit card that you very likely have to pay for medical expenses.
If you still don't know who the custodian is, call the HR department of your School District, because I presume that you have a code W in box 12 on your W-2 - this is the amount of contributions that both your employer and you made by payroll deduction to your HSA - which means that your employer knows who your HSA is with.
