At the top right corner of every post is a post number...if you right click on that and then select 'Copy link address'.
When writing your next post (or editing an existing one) you then highlight a piece of text like 'My V8 Ferraris'
Then click on the link icon that will open up a box, you then paste in the URL using Ctrl+V (like you did with the link to Gustavo's thread above) and click 'OK'
Your bit of highlighted text (that is now underlined and in blue) now acts as the link to that post...as I've done above ^...
Hope this helps....good luck!