What is the difference between Primary and Secondary Succession?

Primary succession is the process by which there are some organisms that have started to grow at a place wherein there wasn’t any organism that was living before. For example, there are some mosses that may start to appear on a rock when it was not there previously.
Secondary succession is the process by which there is a place that has been colonized by other organisms before, but right now, the place has become disturbed or even damaged, so the organisms are not there anymore. This may occur after a natural disaster has taken place. This may also happen when the area has been cleared for something else.