Click menu within the same Main window


Am developing this new desktop app that will serve as an archive or database for keeping information of workers.

  1. First question
    But from my menu
    When I click on any of them, it pops up to a new window instead of working within the same main window. What should I do pls?

  2. Database for my app
    Any suggestions ?
    Since I will create a table to contain details like “Name , Phone, department , date started etc.

  3. How do I make my app fast cos it seems it’s slow to me .

Thank you.