UUs pull from a variety of religious traditions. Some congregations have a very Christian bent - some are more naturalistic - some more Humanist - it depends on the membership and the congregation. Some congregations are lay led - some congregations - like mine, have not only a full time minister, but a staff, hundreds of member families.
We get a lot of mixed faith families - people who thing giving their kids a religious foundation is crucial - but his vague Paganism and her Catholicism can't really compromise outside something like Unitarianism. We get a lot of young former Christians who are rejecting the faith they grew up with, but who want a spiritual experience - and continue to engage in a spiritual search. Unitiarians tend to be politically liberal, so we get people looking for a liberal spiritual experience that engages in relevant Social Action. We are - and have been for decades - GLBT friendly - we were one of the first denominations to perform gay marriages - so we have a lot of GLBT people - and their families - who get angry at the practices of their faith (and some Christian denominations are GLBT friendly - the UCC for instance - we aren't the only option)
There is no creed, there are principals:
http://www.uua.org/visitors/6798.shtml
My congregations sermons are posted:
http://www.whitebearunitarian.org/html/sermons.html For the sake of this discussion - 100 Ways to Pray might be interesting
For our congregation, a service may include Christian hymns or Beatles songs. It likely includes readings from a wide variety of sources - modern poets, ancient writers. About half the time the minister speaks, the other half of the time a guest speaker speaks. There is no communion (as a sacrament for most services - for some services we may use sharing of food as a meditation).
Unitarian Universalists come from two traditions. The first is the Unitarian belief that all Gods are one God. The second is the belief in universal salvation. Both those traditions have their roots in the 17th century - and modern Unitarianism has grown out of that. (The original Unitarian heresy had to do with the Trinity - its a recent turn that takes it towards a Baha'i sort of path - and beyond).
It isn't a faith for everyone. No one is going to tell you what to believe, for Unitarians, its very important that you find those answers for yourself. Therefore, if you like answers and a lot of rules about "you must go to church on Sunday" it isn't a place where you are likely to be comfortable. And that is fine - Unitarians are about discovering your path - not our path (we don't have A path anyway).