Not Safe for Work or NSFW communities has strict rules, and you should be above 18 to view them.
Website:  Log into your account; you will see an arrow pointing downwards in the top right-hand corner. Click on it and go to "User Settings." Now go to the "Feed Settings" option and turn the notch on for "Adult Content."
Mobile: Tap on your avatar at the top left corner and go to "Settings." In the "View Options" section, turn on the "Show NSFW content (I'm over 18) button.