Drupal Community Portal

As a newcomer to Drupal I am considering using it for an application where you have multiple users.
User1, User2, User3 User n... (could be hundreds)
As an example There are 4 tables:
User, account, portfolio, symbol
each user would enter details into the database which are private to them and not available to other users.
This can be easily achieved in a relational databse using tables and foregin keys, then selecting data based on user id etc.
As each user is individual how would I replicate this in Drupal, so each user may be an account holder but they can't see data from another account holder.
Can views seperate the data in this way so that a user when logging on will only see the data they have entered.