Understanding Phases and Turns.

       Each player's turn has five phases, or steps. Understanding what these five phases are and how they work is an essential part of understanding gameplay. In order, the five phases are:

Spoiler:

Beginning phase. The beginning phase has three different steps:
Untap step: the player untaps all his cards unless that cards that are affected by "detain" effect.
Upkeep step: not usually used, but sometimes a player has to pay mana — i.e. tap lands — during this step.
Draw step: the player draws one card.


First main phase. During this phase, a player may put down one land from his or her hand. Also during this phase, a player may choose to play a card from his or her hand by tapping lands to produce mana.

Combat phase.: This phase is split into five steps.

Declare attack: this is where the player first declares attack. The defender may play spells after the attack has been declared.

Declare attackers: after attack has been declared, the attacking player chooses which creatures he wishes to attack with. Attacking player cannot choose which defending creatures he wishes to attack.

Declare blockers: the defending player chooses which, if any, attacking creatures s/he wishes to block. Multiple blockers can be assigned to a single attacker.

Assign damage: creatures deal damage to one another during this step. Attacking creatures with equal (or higher) power compared the blocking creature's defense destroy that blocking creature. Blocking creatures with equal (or higher) power compared the attacking creature's defense destroy that attacking creature. It is possible for both creatures to destroy each other.

End of combat: nothing much happens during this phase; both players are given the opportunity to cast instants.


Second main phase. After combat, there is a second main phase, identical to the first, in which the player can cast spells and summon creatures.

Ending phase, or cleanup. During this phase, any abilities or spells that "trigger" take place. This is a player's last chance to cast instants.
During this phase, the player whose turn is about  to end discards down to 7 cards if s/he has more than 7 cards.