Welcome to the community @Durga_Prasad_Gembali!
The MongoDB Community Server is licensed under the Server Side Public License (SSPL) . As @chris mentioned, the Community Server is freely available and there are also paid options including MongoDB Enterprise (for self-hosted) and MongoDB Atlas (cloud managed).
There is a usage caveat on the SSPL which applies to publicly offering MongoDB as a service. For more information, please see the Server Side Public License FAQ .
There’s also a similar discussion from earlier in the year which you may find helpful: Licensing when it comes to develop commercial applications - #3 by Stennie_X.
Regards,
Stennie