Self-evident means not needing to be demonstrated or explained, it's obvious. The four truths said by Jefferson are: "all men are created equal, that they are endowed by their creator with certain unalienable rights, that among these are life, liberty, and the pursuit of happiness." These truths are "self-evident" to those who understand and want them to be. Everyone understands unalienable rights, however, not everyone believes in them. Jefferson's point was to try and get everyone on board with these ideals, that we are all equal.
