If you are just getting started in the world of precision GPS then I would suggest reading this tutorial from Novatel to get a general overview and understanding of some of the concepts and terms. Even if you are already familiar with the subject, it makes a good review. RTK (real-time kinematics) is covered in Chapter 5 if you want to skip straight there but the rest of the material is worth reading as well.
Here is a nice plot from Chapter 5 of the tutorial showing the relative accuracy of the various GPS methods as a function of the distance between receivers. As you can see, RTK is the most accurate but requires two receivers within roughly 50 km of each other.
For a list of more in-depth material on precision GPS, see the resources page.