what is mtg Lands

Lands represent locations under the player’s control, most of which can be used to generate mana.  Because mana is needed to use almost any card or ability, most decks need a high number of mana-producing lands (typically between 33-40% of the total deck) in order to function effectively.

Playing Lands

Lands are played on the player’s own main phase, when the stack is empty, and only once per turn (though there are spells that can alter how many lands you can play a turn, like Exploration). Playing a land is not like playing a spell; it is a special action that does not use the stack, and does not require passing priority in order for it to resolve. When a player wants to play a land and has the opportunity, he or she simply puts it into play. Likewise, the activated abilities of lands to add to your mana pool do not use the stack, and cannot be responded to. Although many lands generate specific colors of mana, lands are colorless on their own.

Rules

305. Lands
305.1. A player who has priority may play a land card from their hand during a main phase of their turn when the stack is empty. Playing a land is a special action; it doesn’t use the stack (see rule 115). Rather, the player simply puts the land onto the battlefield. Since the land doesn’t go on the stack, it is never a spell, and players can’t respond to it with instants or activated abilities.
305.2. A player can normally play one land during their turn; however, continuous effects may increase this number.
305.2a To determine whether a player can play a land, compare the number of lands the player can play this turn with the number of lands they have already played this turn (including lands played as special actions and lands played during the resolution of spells and abilities). If the number of lands the player can play is greater, the play is legal.
305.2b A player can’t play a land, for any reason, if the number of lands the player can play this turn is equal to or less than the number of lands they have already played this turn. Ignore any part of an effect that instructs a player to do so.
305.3. A player can’t play a land, for any reason, if it isn’t their turn. Ignore any part of an effect that instructs a player to do so.
305.4. Effects may also allow players to “put” lands onto the battlefield. This isn’t the same as “playing a land” and doesn’t count as a land played during the current turn.
305.5. Land subtypes are always a single word and are listed after a long dash. Land subtypes are also called land types. Lands may have multiple subtypes. See rule 205.3i for the complete list of land types.
Example: “Basic Land — Mountain” means the card is a land with the subtype Mountain.

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],” 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. See also rule 605, “Mana Abilities.”
305.7. If an effect sets a land’s subtype to one or more of the basic land types, the land no longer has its old land type. It loses all abilities generated from its rules text, its old land types, and any copy effects affecting that land, and it gains the appropriate mana ability for each new basic land type. Note that this doesn’t remove any abilities that were granted to the land by other effects. Setting a land’s subtype doesn’t add or remove any card types (such as creature) or supertypes (such as basic, legendary, and snow) the land may have. If a land gains one or more land types in addition to its own, it keeps its land types and rules text, and it gains the new land types and mana abilities.
305.8. Any land with the supertype “basic” is a basic land. Any land that doesn’t have this supertype is a nonbasic land, even if it has a basic land type.
305.9. If an object is both a land and another card type, it can be played only as a land. It can’t be cast as a spell.

Basic Lands

The most common lands are the five colored basic lands. Each have the supertype “Basic” (meaning there is no limit to how many cards of that name you can have in a constructed deck,) a subtype matching its name, and a single activated ability allowing you to tap it to generate one colored mana. These basic lands and the mana they generate are: Plains — white, Island — blue, Swamp — black, Mountain — red, Forest — green. When an effect specifically refers to “basic land type,” it is referring to any or all of these five subtypes.

Wastes is a basic land with no subtype. It has an ability to tap for colorless mana.

Ordinarily, changing a card’s subtype does not automatically change its abilities, but the basic land types are an exception. If a land gains a basic land type, it also gains the ability to tap for the appropriate color of mana (and loses all other abilities, unless the type-changing effect allows it to keep its original types.)

Non-basic Lands
There are a variety of non-basic lands (some of which have basic land types).

In general these lands are able to produce multiple colors (i.e. dual lands) or provide a spell like effect (i.e. utility lands). Many of these lands are taplands.

There are some land types associated with non-basic lands.

Desert which was the first non-basic land type introduced.
Urza’s lands and Locuses are able to produce large amount of colorless mana.
Lairs are a set of specific triple lands.
Gates which are associated with the guilds of Ravnica.