Within your
Account Preferences, scroll to 'Receive a notification when someone…'
If you have notifications enabled for when someone quotes your message, you will receive a notification when someone replies to or 'quotes' your post.
Effectively, they serve the same purpose in replying to someone; however, quoting enables you to reply to multiple messages within a single post rather than replying to only one.
Using the messages in this thread as an illustration of this feature for any that may wish to use it:
Select quote for each post you'd like to comment on. It will highlight like so:
Select 'Insert quotes'
Confirm the posts you'd like to add, and then select 'Quote messages'
You'll then have all of the messages you've quoted in your post to easily reply to all of them in a single post
Alternatively, you can highlight specific text in a post and add only your selection to multi quote feature above