Someone dropped a link to a chat in response to a comment (presumably in order to not overload the comment format). But I can't seem to be able to do anything but view that chat. Am I supposed to response in chat, and if so, how?
Talking in chat requires at least 20 reputation points, but you are at 67 so that shouldn't be the issue. All that remains, I think, is to be logged in and on the right page. The chat service is actually on a different set of servers and requires a login separate from (but linked to) your SE site user account.
The page you are looking at may be one of two things:
It may be the transcript page, in which case you need to look for the "join X users in this room" button to jump from the log to the actual chat interface.
It may be the chat interface, but you are not logged in, in which case you need to find the login function to enable the talk features.