They Came from the Pipes

Turning a permanent face up or face down doesn't change whether that permanent is tapped or untapped.

Any time you have priority, you can turn a manifested permanent you control face up by revealing that it's a creature card (ignoring any copy effects or type-changing effects that might be applying to it) and paying its mana cost. This is a special action. It doesn't use the stack and can't be responded to.

You must ensure that your face-down spells and permanents can be easily differentiated from each other. You're not allowed to mix up the cards that represent them on the battlefield to confuse other players. The order in which they entered should remain clear, as well as what ability caused them to be face down. (This includes manifest, disguise, cloak, morph, and a few older effects that turn cards face down.) Common methods for doing this include using markers or dice, or simply placing them in order on the battlefield.