What is the relationship between the mana cost and mana value of a card in the game of Magic: The Gathering?

In Magic: The Gathering, the mana cost of a card determines how much mana you need to pay to cast it, while the mana value of a card refers to the total amount of mana symbols on the card. The relationship between the two is that the mana cost must be equal to or less than the total mana value of the card in order to cast it.