Your question is not clear.
If you are asking about contributions, you are not allowed to contribute to an HSA if you, or your spouse if married, is covered by an FSA.
If you are asking about spending, then you are allowed to spend HSA funds for medical expenses, even if you are also covered by an FSA. But you can't double-dip. Any expense can only be reimbursed once.
When it comes to entering medical expenses on your tax return, you need to ignore expenses that were reimbursed from an FSA, because a medical FSA is not reported anywhere on your tax return (not contributions and not withdrawals). You should report expenses that were reimbursed from an HSA, and those expenses should match your withdrawals from the HSA.
