Most Presbyterian churches in the US are part of the PCUSA. It is not exactly covered by the answers above. It's a mainline church. Its polity is as subscribed, but it accepts modern Biblical studies and theology. That means its theology shares a lot with other mainline churches, such as the Lutherans (ELCA), Episcopal, etc. It doesn't accept Biblical inerrancy, and has more liberal views on gender / sexual issues.
Here's a web page with information about the PCUSA:
http://www.presbyterianmission.org/ministries/101/
Here are our official confessions of faith:
http://www.creeds.net/reformed/creeds.htm
Members vary on predestination. The official position is what I'd call "soft." Most Presbyterians understand that in the end we're called by Christ, and we're his children through no credit of our own. But most don't quite teach TULIP. Here's a statement from the Declaration of Faith (
http://www.creeds.net/reformed/PCUSA1985/1985-int.htm):
The Spirit makes us aware of our sinfulness and need,
moves us to abandon our old way of life,
persuades us to trust in Christ and adopt his way.
In all these things we are responsible for our decisions.
But after we have trusted and repented
we recognize that the Spirit enable us to hear and act.
It is not our faith but God's grace in Jesus Christ
that justifies us and reconciles us to God.
Yet it is only by faith that we accept God's grace
and live by it.
The main body of Presbyterians in the US started diverging from TULIP and other traditional Reformed thought as early as the late 19th Cent. However there have been a number of groups that departed and formed conservative groups. They generally use the Westminster Confession (
http://www.creeds.net/reformed/Westminster/wstmnstr.htm) as a standard, and require officers, and in most cases members, to agree with it to a high degree.
Most participants in this forum are from the conservative churches.
Note that there is a Presbyterian forum here. It's called Confessional, Covenantal, Creedal - Presbyterian. Many of the same people participate in both. You'll get pretty much the same answer if you ask the question there.
This forum covers the whole Reformed movement, which includes both Presbyterian (which historically goes back to England and Scotland) and a set of "continental" Reformed denominations (from Switzerland, Holland, etc.). The Presbyterian forum covers only the Presbyterian groups. Theology is very similar across all of the denominations. There are minor differences in terminology for some bodies within the church. The continental Reformed churches also have mainline and conservative versions.
This group also has members who are Reformed Baptist. While the Reformed Baptists are close to Presbyterian and Continental Reformed, they practice infant baptism, and have other minor differences in theology and practice.