You always have the Charm Person and Mirror Image spells prepared.
In addition, immediately after you cast an Enchantment or Illusion spell using a spell slot, you can cause a creature you can see within 60 feet of yourself to make a Wisdom saving throw against your spell save DC. On a failed save, the target has the Charmed or Frightened condition (your choice) for 1 minute. The target repeats the save at the end of each of its turns, ending the effect on itself on a success.
Once you use this benefit, you can’t use it again until you finish a Long Rest. You can also restore your use of it by expending one use of your Bardic Inspiration (no action required).