Eldritch things are spooky and weird — they make the hairs on the back of your neck stand up.
If you're reading a horror or fantasy story, you may see the word eldritch, which means uncanny, unearthly, and weird in a supernatural way. Anything a witch does is eldritch. Goblins and elves are eldritch creatures. A story full of ghosts and strange monsters is full of eldritch elements. You won't find much that's eldritch in a story about lawyers or doctors. Those kinds of stories are more realistic.