P.8.1- There are two Main phases each turn and they are separated by the Combat phase. Rules that refer to the Main phase (as opposed to First Main or Second Main) refer to the two phases together. [CompRules 1999/05/01]
P.8.2- After triggered abilities are added to the stack at the start of the phase, the current player receives priority to play spells and abilities. [CompRules 1999/05/01]
P.8.3- This is the only phase in which you may cast sorcery, creature, enchantment, or artifact spells, or play sorcery abilities. Only the current player can use these during their main phase. [CompRules 1999/04/23]
P.8.4- During the Main phase, the current player may play a land from their hand if the stack is empty and that player has priority. This special action can only be done once per turn. [CompRules 1999/04/23]
P.8.5- Playing a land is a special action. It cannot be done in response to something and it cannot be responded to. [Duelist Magazine #5, Page 123, 1995/05/01] It has two parts, announcing the playing of the land, and actually putting it into play. This action does not go on the stack. [DeLaney 2000/01/13]
P.8.6- This phase is also called the "Precombat Main Phase". [CompRule 1999/11/01]
P.8.Ruling.1- The restriction of only one land per turn may be overridden by other effects, such as Fastbond, but the rules for playing a land are unchanged. [D'Angelo 1999/05/01]
Note- Many players mistakenly think that the main phase must be ordered as "play a land, then play spells, then attack". You can do these in any order, and it is often good to play it like "attack, then play a land, then play spells". [D'Angelo 1999/05/01]
Note- Remember to check for mana burn at the end of the phase before starting the combat phase. See Rule P.3.5.