This is a very abbreviated explanation:
I've identified as a liberal since the early 1960s, though I took a powder and became apolitical during the late 1960s-early 1970s when liberals were making royal assholes of themselves and poisoning the well.
There's a constant conflict in the West between individual freedom and opportunity on one hand and responsibility to the community on the other. However, I believe that the former needs to be guarded with particular care since the human psyche is all too quick to embrace restrictions and barriers in the interests of security or in response to perceived threats. We have a Constitution that sets forth certain basic principles, specifically equal treatment under the law and IMO the threats to that are lopsidedly coming from the Right at present.
I believe that it's in the interests of the community -- national as well as local -- for all citizens to have access to basic education and health care, that all citizens should be free to marry the person of their choosing (assuming that person is a legally competent adult and wants the same thing) and that the government should make as few laws as possible about choices such as diet, drug use and acceptance of personal risks. I believe in religious freedom; but also believe that the option of freedom from religion has to be part of the package or the phrase "religious freedom" means nothing.
Since 1980 in particular, the redistribution of wealth in this country has been from the bottom up, with a smaller and smaller percentage of people in control of a larger and larger percentage of wealth, and I believe that our elected government has a moral obligation to address that. The current economic chaos can't be analyzed nor resolved by any reductionist approach; i.e., find one villain and slay him. However, I do think that in the past 29 years there has been a regression to the barnyard capitalism of the 19th century, and if a correction means more of what conservatives in general and hate radio screamers in particular call "socialism", so be it.
And if anybody wants to call me a "lefty" or "socialist", they needn't deceive themselves that this is going to bother me at all.