"Liberal Christianity" is a school of thought, or rather a cluster of schools of thought. By its nature, it isn't the kind of thing where you have to sign a specific list of affirmations to be accepted; it's not an official organization where they kick you out if you don't affirm every statement in a particular creed.
In the cluster of "liberal" schools of thought would be Schleiermacher; and Rauschenbusch and a general concern for social justice as an expression of the gospel; and the scholars who do textual criticism and higher criticism; and the theologians who work to bring together the Christian faith with mainstream science, history, and archaeology. (I've probably forgotten some portions of the liberal tradition here.)
It's not as though you have to agree with everything that Schleiermacher, Rauschenbusch, etc., said to be a liberal. I don't know if anyone agrees with all of it; ideas develop and change over time. But if someone said "I'm a liberal, but I think higher criticism is a mistake, and I think the earth is 6000 years old, and we shouldn't ordain women, and the poor aren't the church's business" -- I would suggest that they had chosen the wrong label for themselves.
Does that help?