These services allow users to post questions, share links and answer the questions of other users. Users can also comment on questions or shared links.

Things to discuss and analyze:

Approach to record stats of each answer such as the number of views, up-votes/down-votes, etc.

Follow options should be there for users to follow other users or topics.

News feed generation which means users can see the list of top questions from all the users and topics they follow on their timeline. 

https://www.geeksforgeeks.org/top-10-system-design-interview-questions-and-answers/