Popup message or dialog boxes?

Hi all!
I have an idea for a game.
For the first mission I'd like to have it as an in-game tutorial.. so it'll popup and say use the arrow keys to move.. try it. Then when they complete the task another box pops up with another task to try, etc..

Any idea how I'd go about having these message boxes pop up?

Also, after they do pop up how would I check if the task is completed, some sort of flag in the code?

Thanks for any information.