Primary Succession starts in a rocky area, void of any organisms. Typically, it is a place where an ecosystem has never occurred.
The rocky landscape eventually becomes soil, able to sustain small plants such as lichens. This is called a pioneer community.
From pioneer plants, the landscape then is able to transition from a pioneer community to a climax community.
Secondary succession occurs after the mass destruction of an ecosystem. An example of this is a volcanic eruption.
After the destruction of the ecosystem, it returns to a rocky landscape, as most of the organisms have been killed off.
Eventually, just like in the primary succession, the landscape is able to hold small plants, in a pioneer community. From this, it will grow to become a climax community.