I can read the constitution to get the ideas of those who wrote it just like I can read the Islamic text to get their ideas. To know the exact implementation of the ideas we'd have to study the US law or the law of some other country (and we are sure to see that not all ideas are even implemented in practice). But to learn about the general ideas, reading the original material is actually enough.

And it's actually a good exercise to read both the US constitution and then read Quran and compare the ideas in them.

Let's start with the constitution. I can search through that too.

http://www.usconstitution.net/const.txt

God is never mentioned, religion is mentioned twice:

"no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States."

"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."