Well they're both owned by corporations so really there isn't too much difference nowadays, but basically nowadays, the Republicans have shifted so far to the right that they're way out of touch with the vast majority of Americans, while the Democrats are more centrist but they've also shifted to the right and are basically where Republicans used to be. So basically, today's Republicans are largely extreme right-wingers whereas today's Democrats are largely moderate conservatives.
Now if you want to talk liberals vs. conservatives nowadays, it's different. Conservatives want to force their values on everyone else, they like to pick and choose the parts of the Constitution that suit them (i.e. ignoring the 1st amendment regarding freedom of religious beliefs or the 4th amendment right to be free of illegal searches/seizures, but promoting the hell out of the 2nd amendment to the point where common sense reform is just tossed aside), and are in fact the ones who promote class warfare by continuously lowering and refusing to raise tax rates on corporate profits, capital gains, and dividends while raising the payroll taxes paid by middle and working-class Americans, or the "lazy" as conservatives like to call them.
Liberals on the other hand promote liberty (the root word), freedom, and progress. Medicare, Medicaid, Social Security, civil rights laws, environmental laws, child labor laws, the 40-hour workweek, vacation time, workers' compensation, and greater constitutional protections and liberties are all the result of liberal ideas. Conservatives have the mistaken belief that they can get through life without any help at all, but history and real life circumstances simply don't bear that out. The Constitution provides that Congress's duties include enacting legislation for the general welfare of the American people.