discreet: (adjective) secretive; careful; modest; self-restrained in speech and behaviour
discrete: (adjective) separate; distinct; individual; detached; not continuous
Here are the memory tricks I use to help me decide whether to use discreet or discrete. In discreet, which is used for keeping things quiet, the two Es are close together as if they are whispering in each other’s ears telling a secret. In discrete, which is used for things that are separate, the two Es are separated by a T. Let me know if those tricks are helpful for you too.