It's not anything to do with site permissions - it's where you look!
First, go to the main forum index by clicking on Forum, up at the top left of the screen just under where it says ENZ.
Now, select which forum seems most appropriate to the topic you want to ask about. For instance, if it's about a type of visa, click on 'Immigration', the third heading down. That will bring up a list of the titles of threads in that forum. At the top left of that list, just above and outside the box it's contained in, you'll see a button marked '+ Post New Thread'. There's one of these buttons for each of the forums. Hit that, and you'll get a post screen where you can give your thread a title and enter the message.