You can use your HSA to pay for qualified medical expenses with tax-free dollars. That includes your deductible costs and your coinsurance amount. You can also use it for other qualified expenses as defined in IRS Publication 502 (irs.gov/publications/p502/ar02.html). Any money left at the end of the year is yours to keep in your HSA for future health expenses.
For more information about HSAs in general, visit the U.S. Treasury website: treasury.gov/resource-center/faqs/Taxes/Pages/Health-Savings-Accounts.aspx