When you become a spellcaster, you learn the bare minimum of magic. You learn the Prestidigitation, Thaumaturgy, or Druidcraft cantrip, depending on your class.

"I think it's a perfectly acceptable house rule to grant these cantrips for free to their respective classes. I just think they're so good at fostering creativity amongst the players that they're worth that introduction." - Monty Martin on Dungeon Dudes -  Five Must-Have Cantrips in Dungeons and Dragons 5e @ 24:56