It varies by state and sometimes even county. Sometimes you buy the property outright (a deed), sometimes you buy the debt (a lien), so the original owner pays you back with interest but they keep the property unless you foreclose, and sometimes you buy the right to the land if the original owner doesn't pay you back within a set time frame. (a redemption deed)

Here's a general map of how it works, by state: https://www.secretsoftaxlieninvesting.com/tax-sale-map

In general, when it's sold as a deed, and sometimes as a redemption deed, non-government liens on the property are forfeit, and it clears out the taxes owed by the government entity selling it, but it doesn't clear out other government liens, e.g. when a property is sold to pay county property tax, the federal government could have a lien on it for income tax owed by the same owner, and the county could have a lien on it for sidewalk repair, and a mortgage company could have a lien for a loan. The mortgage company would be unable to collect anything, the federal tax lien would likely allow the government to force you to sell it to them for what you paid for it, but they wouldn't be entitled to collect from you, because it's the previous owner who pays taxes, but you could still be required to pay the county lien for sidewalk, plus penalties accrued since the previous owners non payment started, because you now own that property and its sidewalk.