Any cards you don't play will remain exiled.

The cards are exiled face up.

Under normal circumstances, you can play a land card exiled with Commune with Lava only if you haven't played a land yet that turn.

Playing a card this way follows the normal rules for playing the card. You must pay its costs, and you must follow all applicable timing rules. For example, if one of the cards is a creature card, you can cast that card only during your main phase while the stack is empty.