Where do I go to ask questions?

Hello, I have a question. When I go to play online and select the type of game, there is one that sais recent, and has this pin and unpin button. I am confused and want to know what this is and how to get rid of it.

My chess board is black if I want to play or continue a daily game but not for puzzles 

I  am unable to see the pieces 

So change the board color or the pieces color.

You can change them in settings.

https://www.chess.com/settings/board

How is this move brilliant?

You're allowing the bishop on c4 to be captured (as sacrifice) and the move must either be best or good. It's not a true sacrifice, since the material can be regained easily but depending on the rating of the player, it must meet the classification criteria.

He can't use his h pawn, because it is pinned against his king by the black rook on h4.

He has the option to capture the bishop on g4 with his queen or to move the queen. If he moves the queen away, he will lose the knight on h5.

If he takes the bishop with his queen, the queen will be giving check, so black will be forced to take the queen with the rook and the rook can then be captured by the h pawn.