Any comments left on posts on the newsfeed are publicly visible.

You'll be able to see the top few comments and their authors while scrolling the newsfeed, but clicking the grey speech bubble under the reactions bar reveals a full comments screen.

A number count, as well as the name of the most recent commenter will be visible from your news tab.

Once you're on the full comments screen you'll also be able to react to comments other users have added.