In a lot of ways the big difference between Hillary Clinton and Bernie Sanders is their willingness to spend government money to help the middle class. Hillary Clinton is a representative of the current Democratic status quo: tax the rich a little, and use the money you raise to fund some programs benefiting the poor. Sanders on the other hand wants to tax the rich a lot, and the upper middle class a little, and use the money to fund programs benefiting the whole country.
The Bernie model is more expensive in terms of how much tax revenue it requires, but does more good both per dollar spent and in total, because it’s just a more streamlined, efficient way to do things.
Hillary wants the status quo of Obamacare: the poorest get Medicaid, the lower middle class gets subsidies, and everybody else buys insurance on the private market.
Bernie wants universal healthcare: one big government system that needs more tax revenue, but also gives free health insurance to everyone in America.
Hillary wants programs to help the poor afford college, and to help out students who are having a particularly hard time paying their debts. Everybody else continues to pay the spiraling out of control tuition.
Bernie wants free public higher education for everybody who qualifies and is interested.