Alok,
Say your main application tcode is A and you have another tcodes b c d which is called inside A and can be called directly as well
you can achieve this by
1. setting a memory and pass the entry t code to the application and store it eg: so while u enter in the application the value will be say A
,2. Now u enter in your application. For each t codes at the begining, Import the memory and check whether the tcode value is A if yes proceed else throw an error message
3. If some one enters the tcode directly, the memory value will be empty, so your check fails and he gets an error and cannot proceed
Further you can validate the user id if you wish to restrict the users in the application entry point
