Hi Lianne!
Yes - you can do that. Look at your post here - up in the upper right, you'll see a little #1 - you can right click on that and choose "copy link location" (or something similar depending on your browser) and then go to your new post and right click and paste the link. That will be a link directly to a single post, which can be very helpful and save time
If you want to post a link to the whole thread, just navigate to the thread you want, go up to the address bar in your browser, and copy the whole link. Then paste it into the new thread.