Theme Directory Confusion

sHi everyone.

I am new in Drupal and trying to create my own theme.

After reading few articles from some websites, I am confusing to create my theme under which directory.

Some articles write should create under /core/themes and some write /themes, so where should I create my custom theme?

What the difference between these two directories?

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/3/feed