C# Ads API Access


I am accessing ads apis. It uses 3-legged authentication and requires user context. I am not able to understand how to get user context. I am able to get application context using consumer key and secret.
But for user context we need something more? kindly help. I am using C# to build application
If you know any 3rd party apps which can generate token based on consumer key, consumer secret, access toke, access token secret. let me know. I am new to this.