Lands you control are Plains. Nonland permanents you control are white. The same is true for spells you control and nonland cards you own that aren't on the battlefield. You may spend white mana as though it were mana of any color. You may spend other mana only as though it were colorless mana.
"The days before the war were filled with strange portents: scouts and herders spoke of villages reduced to ash, of farmers taken from their fields, and of foul beasts roaming the plains in packs. I know, for I spoke to them all." —Hakim, Loreweaver
You gain 5 life. When a spell or ability an opponent controls causes you to discard Mangara's Blessing, you gain 2 life, and you return Mangara's Blessing from your graveyard to your hand at the beginning of the next end step.