Stop trying to write it all at once, and think about what you are doing and the data you need to store.
You have a User: so create a basic class for him.
public class User
{
public string Name {get; set;}
public string Id {get; set;}
}
Now write code to hold a collection of users, and then write a method to add new new user name and ID to it.
Write code to print the user details.
Now write code to main to add a number of users by calling AddUser several times, then use your print details method to show it works.
Test it.
Then repeat the process for the Note and Category classes.
When they are all working, add the Note and Category collections to the User, and add the code to support them.
Do it a stage at a time, testing as you go so at each stage you know that what you are working with is correct.
This may help: help:
How to Write Code to Solve a Problem, A Beginner's Guide[
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