What is the relationship between lands and mana in Magic and what do each of them do? A good answer should especially include how a new player should think about them.
Note:
This is an attempt to create a canonical question about the relationship between lands and mana in Magic.
Beginners are often confused about this given the same symbols are used to mean different things across basic lands, non-basic lands, and mana costs. This can lead to confusion about lands being mana, about non-basic lands putting basic lands into play, or even about what mana is.