Hello again, Judy.
Yes, you can join in on any thread, on any particular crossword. Usually people post queries, ask for help - but sometimes it's just a comment on the puzzle. If you have a query, it's always good to look to see if your puzzle, Private Eye 123 say, already has a thread - sometimes the answer you need will have been given already. If there's no listing - on the front/first page of the Forum - you can start a thread. The title should be Times Cryptic 101, then everyone knows which puzzle it is.