1. A Firebolt: This is the main broom, a top-of-the-line racing broom that Sirius gifts Harry for his birthday.
2. A secondhand broom: This is the broom Harry was using before receiving the Firebolt. It's not specified what kind of broom it is, but it's implied to be a fairly basic model.
So, Sirius gave Harry two brooms in total, though the Firebolt is the one that gets the most attention.