Hii Shivani!

If you read the class 12th Biology NCERT textbook carefully, in the unit ecosystem, you will get to know well about the primary and secondary succession. Primary succession starts on a barren land where the pioneer species are lichens and small microorganisms. It takes several years , even centuries for a primary succession to reach climax.  Example- hydrach to mesarch condition.

Whereas Secondary succession occurs on a place where once their was life but was distroyed completely due to some reasons. The secondary succession is fast as compared to primary succession. Example- xerarch to mesarch condition.

To get an elaborated detail, you may refer to textbooks such as S.chand or dinesh publications.

Hope this helps.

Good luck!