The JUnit tests in Jonathan Hedley's JSoup Repository are an excellent resource for learning JSoup and seeing it in action.
Here's some example code:
@Test public void testAllElements() {
String h = "<div><p>Hello</p><p><b>there</b></p></div>";
Document doc = Jsoup.parse(h);
Elements allDoc = doc.select("*");
Elements allUnderDiv = doc.select("div *");
assertEquals(8, allDoc.size());
assertEquals(3, allUnderDiv.size());
assertEquals("p", allUnderDiv.first().tagName());
}