The IT Department allows medical reimbursement of up to Rs. 15,000. You need to furnish the necessary bills to your employer to claim this. The remaining part of your unclaimed amount from the Rs. 15,000 is added to your taxable salary.
And your taxable salary is taxed at the slab rate you belong to. The bills must be between 1st April last year to 31st March this year(pertaining to the FY you're filing for).