how to retrive sharepoint list data in c#.net project?

tejaswini1010 PnP sites core library is by far the easiest way

https://github.com/SharePoint/PnP-Sites-Core/blob/master/Core/README.md

Samples: https://github.com/SharePoint/PnP/tree/master/Samples

You can also find great code samples if you search for PnP sites core online:

For example (selected randomly): https://www.c-sharpcorner.com/article/sharepoint-online-list-operations-using-pnp-core-csom-library/

Hope this helps