Takeing photo of horse raceing

That depends on what you want your photos to say to the viewer. You can use a fast shutter speed to freeze the action, or you can use a slow shutter speed and pan with the horse to convey a sense of motion.
The camera is a tool. You're the photographer. It's up to you to decide what you want to do with the tool. Four photographers at the same place and time with the same camera will come away with four different sets of images.