If you have a custom record existing on your account and you would like to create a new record of that custom record and you wish to do this via C# the following code will show you how to do that.
Please note you will need a valid login session.
// Creating a custom record object.
CustomRecord myCR = new CustomRecord();
// Creating a RecordRef object with the internal ID of 2
// the internal ID is the ID of the custom record existing in your account.
RecordRef rf = new RecordRef();
rf.internalId = "2";
// Applying the RecordRef object to the Custom Record object.
myCR.recType = rf;
// Adding the custom record into NetSuite.
WriteResponse res = nss.add(myCR);
// Checking to see the status of the custom record being added to NetSuite.
MessageBox.Show("Daily Activity created.");