The supreme court of United States usually functions as an
appeals court as it hears all the appeals from other courts below
it.
These lower court's who take their appeals to the supreme court
might be trial court's.
That is, the supereme court has the orginal jurisdiction or
authority to hear all the appeals and make a final decision.
The appeals of changing anti trust laws, labour laws etc are
taken to the supreme court of the US as it has the final and a
critical role to play in shaping the economy.