Very little in the end. At common law, you are done for at once. In Equity, you are not so easily disposed of. The former is a bullet which is instantaneously and charmingly effective. The latter, an angler's hook, which plays the victim before it kills him.
Common law is acid, equity is opium.
American law can be federal or state, depending on the subject matter of the law. The power to write laws in the USA has been divvied-up in the American Constitution. So, some legal issues can be described and the information would apply from Bangor to San Diego. If you can't find what you're looking for here, try the USA-wide Law Pages . But other matters are subject to state laws and, as such, may vary from state to state.