What error you are gtetting?
You can refer below code for your refrence -
string strName= "TestData";
SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ToString());
SqlCommand cmd = new SqlCommand();
cmd.CommandText = "INSERT INTO YourTableName (YourFirstNameColumnName) VALUES (@FirstName)
//Uses the FirstName variable and creates a new sql variable for use in the sql commandtext
cmd.Parameters.Add("@FirstName", SqlDbType.NVarChar).Value = FirstName;
cmd.Connection = conn;
conn.Open();
cmd.ExecuteNonQuery();
conn.Close();