When I think of conservatives, I think of two things. Fiscal conservatives (ie, people who seek to spend money carefully) and Social Conservatives (ie, people who seek to preserve a traditional way of life that they view as ideal). People can fall into one category or the other, but historically, Republicans have mostly focused on fiscal conservatism, and have also played a role in conservation of land and air through votes on national parks and support for the EPA. Since the Reagan years, however, Social Conservatives have blurred the divide, and many Republicans have abandoned fiscal conservatism for "family values" issues like protecting marriage, overturning abortion laws, and injecting religion into our government. The Libertarian Party might be considered a pure fiscally-conservative movement.
Liberals are on the opposite extreme. Fiscal liberals advocate for the creation of government programs to solve social problems like access to health care, the creation of a safety net for the elderly, disabled, unemployed, single mothers, etc. among us. They believe in spending money 'liberally' to create an acceptable living standard for every citizen. Social liberals advocate for the change of traditional ways of thinking and doing things to even the playing field socially. They support gay/lesbian rights, minority rights, abortion laws, and liberal immigration policies to help ensure that everyone has a similar experience and quality of life. Liberal-Progressives are the most extreme kind of liberals, encompassing both kinds of liberalism.
Most of us in America, if pressed, are fiscally moderate. Unfortunately, we've been pushed to the political extremes by social issues (which carry more emotion), and tend to ignore the more important money related stuff.