A simple way to get started with macro photography is to use your existing lens with either a teleconverter or a focusing tube.
The attached video tutorial demonstrates how to use these.
The images taken whilst making the video are shown below for reference, showing how the magnification is produced. Whilst not necessarily being among my best shots, they do illustrate how you can get good images using this simple set up. The lens I used with the focusing tubes was a Canon 17-40mm lens.
1) Image with Focusing Tubes. ISO used was 320, Aperture F8 giving a shutter speed of 1/320th second.
2) Image with 2x Teleconverter. ISO used was 320, Aperture F6.3 giving a shutter speed of 1/200th second.
3) Image with 100mm Canon Macro Lens. ISO used was 320, Aperture F6.3 with a shutter speed of 1/200th second.