I'm a newby here on GOG. My question (s) are platform concerns. 1.) When you purchase a game can it be played on different devices ? If so, what platforms? 2.) Can games be played on tablets without controller's? Is there info you can direct me to so I can learn more?

Each game has a system and hardware requirements for it to run in its description. When it comes to ability to play on different computers - yes - any computer you own and follows the hardware/OS requirements can have your game installed on it.

1) There are no restrictions of where you play as long as you have legally transacted; and you can take that a step further with offline installers. (See the dropdown arrow on the left of the game card.)

2) That really depends on the game. You're not getting far in a game like Factorio on a tablet.