Fusion 360 is a great piece of design software. It's made by Autodesk and is currently free to use for Home users. Just register on their website and when you download / install choose the Startup option.
Lots of youtube getting started videos are available, here is one of them....
So.. what are you waiting for :-)
First go and download it from.. http://www.autodesk.com/products/fusion-360/overview
Then download the trail, when you install it choose the startup option so its free :-)