I would like to Trigger an email using data extension. Data extension and Triggered Send is already created in Marketing Cloud UI. How do we trigger the email in C# using SOAP API? Do we need to multiple SOAP API calls or single SOAP API call to Marketing Cloud to trigger the email?
It's a single API call. The official documentation should get you going in the right direction:
The Data Extension needs to be created with the Triggered Send Definition template. It should not have a Primary Key.