How to get villagers: Villagers spawn in three ways. First, they naturally spawn when villages are generated. Second, villagers can breed and have babies, which grow up after 20 minutes. Third, zombie villagers can be cured with a weakness potion and a golden apple. This is useful for starting a new village.
Dangers to villagers: Zombies will naturally attack villagers, with a chance of turning them into zombie villagers. This chance is 0% in easy, 50% in normal and 100% in hard. Vindicators, Evokers and Illusioners will naturally attack villagers as well. Villagers can also be turned into witches if they are struck by lightning.
Creepers + Boom Slimes = Big Crater
Minecrafting all the time!
I post too much.