What do I have to do?
Do I get paid? Like with real money?
Do I get credit for the game?
Do I have to move?
What is my part in making this game?
Do I need to sign something?
Are you really making my game?
Most of these answers are in the Terms and Conditions for idea submission at: https://www.brightlocker.com/imagine. Specifically read parts 3 through 10 as those deal with Shares, Promotion, Participation, and Credit. While in it's entirety it may seem like a boring read, it really should be understood by all submitters and has important information for submitters with games in production throughout.
With that said below are some very short, incomplete, non-comprehensive, plain speak answers to those questions above.
Qs. What do I have to do? What is my part in making this game? Do I have to move?
A. Do nothing if you want. The hard part is done and your game was picked. Participation in the process will vary from submitter to submitter. Have more to include... let's have a meeting or two or 100. Gave all the ideas you have... sit back let us do all the heavy lifting. No moving necessary.
Q. Do I get paid? Like with real money?
A. There is a good chance of that. The short version is after the game is made and we start selling it, you will get a portion of that revenue.
Q. Do I get credit for the game?
A. Yup! Yes! Absolutely.
Q. Do I need to sign something?
A. Technically you already did. When you submitted the game and accepted the Terms and Conditions. There may be other things down the road (tax season most likely.)
Q. Are you really making my game?
A. If the game idea you submitted was picked during a Grand Final... we certainly are making your game.