Do cardano has rest apis which i an integrate with the third party cms?

I am wondering that do cardano has rest apis which i could integrate directly with the third party cms for example an api to create a wallet and an api to sent funds etc? if not how can i go ahead and create some of those?

For interacting with the blockchain, there are, for example, https://blockfrost.io/ or https://api.koios.rest/.

For managing keys and building transactions, you can use: https://github.com/Emurgo/cardano-serialization-lib

Is there postmon documentation as well?

For koios and blockfrost, the documentation is at the links above.

For CSL, I haven’t really found a proper documentation, just some examples flying around in that github. The most complete list of what is possible seems to be: https://github.com/Emurgo/cardano-serialization-lib/blob/master/rust/pkg/cardano_serialization_lib.js.flow It is also the only thing linked from: https://docs.cardano.org/cardano-components/cardano-serialization-lib

Note postman is just a fancy UI veneer on top of HTTP requests and responses. Any HTTP, REST, etc API will be compatible. If you see examples using the more popular curl utility for command line then simply use the import feature of postman, it should be able to interpret this as I recall it being able to export curl commands once up on a time when I had to use it.