How is the panel configured?
Just drag the blueprint from the Panel into the world, and you're done.
Then you can customize whatever you need: distance between buttons, sizes, height, width, sounds, whether you want to see the top panel or just want buttons.
How is the password entered checked?
The checks go in order, from left to right. It's as simple as activating the positions you want to press the buttons.
Interface
An interact interface is also included. You can use it so that, upon completing the puzzle, the interact event of the selected actor is automatically called, or you can also use the “CorrectPassword” dispatcher and have your actor listen for that event.