When can lands be tapped?

Question

I'm completely new to Magic the Gathering. I've read the basic rulebook pretty thoroughly and have a pretty good grasp of the basic rules, but it's unclear to me as to when you can tap lands to generate mana.

First off, mana is supposed to dry up after each phase in a turn. Can I untap my land cards and then tap them again in the next phase if I need more mana to power a spell? Or does a land card remain tapped until my next turn like everything else?

Second, the rules mention that I can play instants and activate abilities during my opponent's turn. Does that then mean that I can tap my land cards during my opponent's turn to power those spells?

Third, does my opponent's untap step for their turn only apply to their cards? Or can I untap mine as well? Not closely related to land cards, but when I can tap and untap my land cards would make a huge difference as to how I play.

Hope these questions aren't painfully obvious, but I've just started playing the game. Thanks for your time!

Answer 1

You can tap lands for mana at almost any time. Pretty much any time you could do anything else, anyway. Among other things, you can tap land for mana any time you want to play a spell or ability and you need mana to do so.

You can only untap a land when you untap your other cards during YOUR untap step (or if a spell or ability instructs you to untap a card). So no, you cannot untap your lands after each phase when the mana they produced goes away, or during your opponent's untap step.

So without getting into the specific details of the comprehensive rules, which would just cause confusion for beginners, what you really need to know is that you can tap a land any time you need mana, and your lands will normally only untap at the beginning of your turn.

Relevant rules from the Basic Rulebook:

Under "Casting a Spell"

Now check what the spell’s cost is. Tap your lands to produce the mana necessary to pay that cost, and pay it.

Also note that mana will empty from your mana pool at the end of every step, not just at the end of each phase. Each phase is divided into multiple steps.

Answer 2

Lands may be tapped at any time for mana, though it's usually pointless to do that when you aren't casting a spell or activating an ability.

What actually happens is there is something called your "mana pool". This is what is actually emptied at certain phases. The appropriate ruling is as follows:

305.6. The basic land types are Plains, Island, Swamp, Mountain, and Forest. If an object uses the words "basic land type," it’s referring to one of these subtypes. A land with a basic land type has the intrinsic ability "{T}: Add [mana symbol] to your mana pool," even if the text box doesn’t actually contain that text or the object has no text box. For Plains, [mana symbol] is {W}; for Islands, {U}; for Swamps, {B}; for Mountains, {R}; and for Forests, {G}. See rule 107.4a. Also see rule 605, "Mana Abilities."

The basic lands are permanents that can add to your mana pool. Since this is an activated ability, it can be used during your opponent's turn. Other than that, though, they ordinarily untap during your turn at the same time as everything else. Technically, the order of casting a spell is as follows:

1. Tap cards to add mana to your mana pool
2. When the spell is played from your hand, it subtracts the appropriate amount from your mana pool.

Until Magic 2010, having excess mana at the end of your turn would cause "mana burn", which does damage to you equal to however much is leftover. The Magic 2010 rules changes did away with this.

Answer 3

You can however tap a land at the beginning of your turn use the mana cast a spell then still untap it during your untapp phase. I think. I used to run a squerrel deck with a herd gnar it's a (2)g or (3)g I forget 2/2 creature that whenever a creature comes into play under your control herd gnar gets +2/+2 until end of turn. So I would use my lands at the beginning of my turn to cast instants to put out creature tokens then untap during my untap phase and cast more tokens.