I've been using steem since mid May, and I didn't know about this until recently. Because I didn't know, you might not either.
There is a eSteem app, which I downloaded onto my iPhone when I first got info steem. By default, the notifications are turned off. You can, however, turn them on! You can then see notifications when events like people following/unfollowing you, people mentioning you with the @name or people replying to you. It's super handy, and makes steem more functional and useful, in my opinion.
There's a longer post that goes into details here:
https://steemit.com/steemit/@scrooger/steemit-notifications-where-or-how-or-why
Good luck and steem on!!!!