What programs can I use on Windows 7 to play my game?

What do you mean? Did you build the project in the engine? Then it should’ve outputted a folder with a .exe file to launch the game.

I have finished my game and have put it onto a flash drive. On my Windows 7 computer, it says that there is no program that can open my game. Is there any program that I can download to open my game? If there is, please tell me.

No it just came up as a .uproject file.

No it just came up as a .uproject file

That’s your project, not your game. You need to package your game from the editor to produce files you can run in other PCs:

http://i.imgur.com/NgJVehQ.png