At its core, Conservatism is based on the ideas of the founding fathers, perhaps the greatest group of men ever gathered together in the history of the world. Freedom derived from the Creator, a decentralized federal government with specific enumerated powers, and individual liberty protected from the tyranny of the majority. No matter what differences conservatives have with one another, we share these basic principles in common. (Note however there are certainly atheist conservatives, most notably Ayn Rand.)
The first point, "freedom", does not only include those specifically listed in the Bill of Rights. Speech, religion, the right to assemble, these are all important freedoms, but as the 9th Amendment States, they are not the only ones. Conservatives believe in the concept of "economic freedom". Every man (or woman) should be free to make as much (or as little) as their faculties allow. When Jefferson wrote "We hold these truths to be self evident that all men are created equal", he was talking about the basic rights that all men are endowed with. Equality in birth, not equality in outcome. With freedom comes responsibility, and each man should be responsible for himself. A man has no right to infringe upon his neighbor's economic freedom in order to further his own.
In order to protect this concept of freedom, the founders (through the Constitution) imposed strict limits upon the Federal government. Conservatism seeks to bring the ever growing Federal government back into this Constitutional framework. States were not always the provincial administrative units they are now. They were once sovereign and free. For the purpose of common defense they entered into the Articles of Confederation. When this union proved too weak, the founders drafted the Constitution, and the individual States ratified it. However, while this created a more solid and defined Federal system, with a stronger central government, the present size and power of the Federal government was NEVER envisioned by the founders. I dare say it was the very thing they most feared.
Conservatives seek to restore the original balance of the Federal system and are thus advocates of States Rights. Local governments are far more responsive the the people and act as a check on a tyrannical trending central government. The founders understood this better than we ever can, and Conservatism seeks to restore the original powers of the State, at the expense of the Federal government.
The Constitution once limited the government. As strict constructionists, Conservatives wish to return to the original intent. The Constitution is not a "living, breathing" document that evolves over time. It is a legal document that created a Republic unable to infringe upon individual liberty. Now that it is seemingly ignored, the majority is free to infringe upon the liberties of the individual, just as the Federal government is free to infringe upon the rights of the State. So at its core Conservatism is an ideology of limited government and originalism.
This is certainly not all there is to Conservatism, books have been written about Conservatism and its stance on far more issues than I have elaborated on. This is just the basic structure of the Conservative philosophy and ideology. This is the America the founders envisioned, and men like William F Buckley, Barry Goldwater, and Ronald Reagan sought to restore.