I believe that there is no IT professional, who did not use GNS3 at least once. I use it almost every day. It is pretty easy to use it for pure networking simulations, but if you want to use it for PC or server emulation you need VirtualBox.
You can download GNS3 from this location. First create your virtual machine on VirtualBox. I have installed Korora, Fedora distro for desktop users (Slide 1.).
Now start your GNS3 installation. As you can see I already have some end devices imported (Slide 2 & 3).
Now select Edit – Preferences… . Select VirtualBox from General on Preferences page. Select then option New and pick virteal machine from drop down on New VirtualBox Virtual Machine page (Slides 4 – 5 – 6).
Your VM Template will appear in list (Slide 7.). Now you can drag and drop your new VM to working area in GNS3.
I hope that this tutorial was informative to you and thank you for visiting this website.