How to create an ajax newsfeed?

Question

Feeds

There is a site with the addition of posts and there is a feed of these same posts. Any user can subscribe to other users' updates, and subscribe to certain tags. In the news feed, respectively, posts of users to which the user is subscribed, and posts with tags to which the user is subscribed should be displayed. Moreover, these posts should be sorted by date of addition and displayed in 20 pieces. When the user reaches the very bottom of the page, another 20 posts will have to load.
How can this be implemented?