Saint Elenda is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Lifelink When Saint Elenda enters, conjure a card of your choice from Saint Elenda's spellbook into your hand. You may cast that card this turn without paying its mana cost. At the beginning of your end step, if you gained life this turn, create an X/X white Avatar creature token, where X is the amount of life you gained this turn.