Macro lenses are the up close and personal tools of the photography world. Mere close-ups aren't good enough: Macro lenses let us take extremeclose-ups of subjects while keeping a photograph in tight focus. Macro lenses bring the focal point of a camera closer by extending the amount of space between the camera sensor and the lens aperture. This means shooting with a macro lens requires setting up as close to a subject as possible. That can be difficult with insects or other subjects that tend to move around, but plants are usually pretty good about staying put.
Macro lenses provide magnification that you can't get with a telephoto or wide angle lens. Technically, real macro lenses are able to reproduce a subject at a 1:1 ratio or better on the camera's image sensor. The lenses are commonly used to produce those sometimes creepy, sometimes amazing close-ups of insects. Using a macro lens in flower photography allows photographers to fill the entire frame and reveal details we'd never notice with the naked eye.
To get an amazing macro photograph, you'll have to be ready to buy an expensive macro lens. If you're not ready to commit $500 or $1000 to a lens for your flower shots, there are some cheaper alternatives. Macro extension tubes sit between the lens and the camera, and close-up lens filters screw onto the end of a camera lens. Both can help bring the camera's focal distance closer to the lens to allow for macro-style photographs.