Well, the basics are quite simple. In junit 4 you annotate your test methods like the following. Your class doesn't have to extend anything.
public class SimpleTest {
@Test
public void aTestCase() {
//Some test code...
}
}
In Junit 3 you method name has to end with Test and the class has to extend TestCase.
public class SimpleTest extends TestCase {
public void aSimpleTest() {
//Some test code...
}
}
I would recommend starting with Junit 4 right away. It's easier in my opinion. Especially when setting up test suites. Just google Junit 4 tutorial.
Regarding netbeans and other IDE:s, There are probably plugins that make creation of test classes and stuff a bit faster, google that.