am trying to create a brochure in Photoshop. But how do you get such a folded effect i.e. when I want to show the brochure to someone else as a preview, I want to make it look as if it's folded (like in the image below):
You can easily get that by using a mock up. Just download it and place your picture in the layer which they mentioned.
what Rijin mentioned is actually correct.
Normally for designers first we design the draft, & then we would actually find some nice mockup template to show the client so that they can visualize how are the actual print outs going to look like as a preview. This is quite common in our company here so that we can save time & avoid misunderstanding on both sides.
For me i personally use http://graphicburger.com/ for mockup resources. Download the mockup which you find suitable & replace the content by double clicking on the smart object layer.
I hope this helps. :)
I have also resorted to using premade mockup PSD files to show clients, because I don't want to spend the time creating my own. (even though the sample mockup doesn't show the 6th panel).
If you grab a mockup from someplace, you'll notice that there are one or more layers with "editable" content (clicking on the layers will open an embedded photoshop file, sometimes nested 2 levels down, where you replace their artwork with your own)
Those layers on the mockup file are treated with layer effects, shading, and distortion to yield a realistic look.
all the above answers are applicable. but none of them mentioned "photoshop action" .. simply you can download a free photoshop action from tons of it online ... simply you can select the way your folded brochure would look like and place your design over a template then run the action and that's it.
if those link are dead in the future, you can google "folding brochure Photoshop action" if not you may use a preset action or just do your own action.
and what is a photoshop action? it is a list of commands and transformation values you can do by yourself as if you are doing the folding brochure from scratch, a step by step. like dividing your design in three layers and preposition and rotate every layer to take the effect of a real folding brochure, and by adding some shadow and light effects.
Google "Brochure mockup PSD" or "trifold mockup PSD" and you will find many free and premium (paid) options to create mockup your file like the image you included. I use these frequently for my portfolio.