(Centaur Flagstones isn't a spell.)
Centaur Flagstones enters the battlefield tapped unless you pay 2 life.
All creatures have protection from red.
: Add or to your mana pool.
Put Centaur Flagstones on top of your library: Add to your mana pool.
: Add 
or 
to your mana pool.
to your mana pool. 
