About Trusted_Connection

Question

Can anyone tell me about how to use Trusted_Connection? I have my Connection String with the "Trusted_Connection=true" but it returns the error message below: "System.Data.SqlClient.SqlException: Login failed for user '(null)'. Reason: Not associated with a trusted SQL Server connection." How should I handle with the problem? Or there is something I haven't done to make it could operate? Please help me. I know the question looks stupid, but I do need someone to tell me.