To attach a thread, open another window, navigate to that thread, then copy what appears in the address field at the top of your browser screen. Then go back to your original window and paste it in your response. For example - if I wanted to paste a link to this thread, I'd copy and paste the address http://chowhound.chow.com/topics/804372 from the top of the page.
To create a link to a specific post within a thread, go to the thread, then go to the post you want to link, and click on Permalink at the bottom right of the post. Then do exactly as before, but you'll notice that the text string is now longer as it contains the address of that specific post within the thread. So, for example, the Permalink to your own post above is http://chowhound.chow.com/topics/8043...
Practice a couple of times and you'll have it down pat.
If you know how to copy and paste then you simply copy the URL of the thread you are reading which shows in your browser window (of the thread you want to "share" with others) and then, when you are writing your reply on some other thread you then hit paste in the message box and the URL for the link should then show up and become a hyperlink in your reply after you hit "post my reply" Does that make sense to you?
Just as a quick example - if I wanted to share this thread you commented on regarding "Mariscos Chente" from the Los Angeles board I copied the URL and then pasted it here http://chowhound.chow.com/topics/797564 and it showed up as a hyperlink that allows anyone to click on it and get taken directly to that thread. If I wanted to single out just one of your posts from that thread to share then I go to that same thread and go to your post and hit "Permalink" and then copy and paste that URL here http://chowhound.chow.com/topics/7975... and it will take anyone directly to that single post by you.