Hi Abinaya:
We can't really answer Salesforce specific questions, but other people have successfully integrated with the DFP API using Salesforce before.
For authentication, you will need to be able to use OAuth2 with Salesforce to authenticate with the DFP API. You can probably find more information on how to use OAuth2 with Salesforce in the Salesforce documentation, but here is DFP's auth information:
You will most likely need to generate the SOAP payloads yourself using Salesforce (Apex), here is DFP's guide on our raw SOAP payloads:
If you run into issues generating raw SOAP, we generally recommend that you download one of our
client libraries, use them in an environment outside of Salesforce (like your local machine). Enable logging and make an API call then examine the SOAP logs to see what the properly formatted SOAP XML should look like if you are having issues generating it.
Thanks,
Vincent Tsao, DFP API Team