If a card in a player's library has {X} in its mana cost, X is considered to be 0.

If a permanent card in your library has no mana symbols in its upper right corner (because it's a land card, for example), its mana value is 0. Such cards can always be put onto the battlefield with Genesis Wave.

A permanent card is an artifact, battle, creature, enchantment, land, or planeswalker card.

If you have fewer than X cards in your library, you reveal all of them.

All of the permanents put onto the battlefield this way enter at the same time. If any have triggered abilities that trigger on something else entering, they'll see each other.

You don't have to put permanent cards revealed this way onto the battlefield if you choose not to, regardless of their mana values.