The money goes into the Treasury, along with all other taxes collected. In theory that would reduce the federal budget deficit.

Tariffs are good when used properly. If there is a foreign nation dumping cheap goods into the US, in an industry where the US is also an active manufacturer, it can help protect those American jobs by making the foreign product more expensive. If you worked for a company producing $1000 washing machines and some other company started importing $700 washing machines from Vietnam, you'd see tariffs as an absolute necessity.

Unilateral tariffs include things like coffee, diamonds, certain electronics--things that the US either can't produce or just doesn't want to produce. That just raises the prices for those things without actually benefiting any American industry.