What are the differences?
On foreign policy, not much. Both parties have historically believed in free trade, US hegemony and exceptionalism, capitalism and free markets as the answer to the world's ills, and spreading democracy as a good in itself. Trump is an exception, claiming to be isolationalist, and against free trade just for the sake of free trade, and believing in America first.
On domestic policy, there are many differences: Republican policy has usually included: lower taxes, fewer regulations on companies, no abortion, less social welfare for the poor, fewer restrictions around gun ownership, fewer rights for LGBTQ, and so on. Democratic policy has included: higher taxes to pay for social programs for the poor, restricted gun ownership, more regulations on companies, free access to abortion, equality for LGBTQ, etc.