Hi - There are multiple modeling workflows that will get you to your goal fairly quickly. That said, without making assumptions about your comfort level with CAD I might suggest the following progression;
#1 Leverage the community - Start by searching thingiverse, youmagine, grabcad,etc. and seeing if someone else has made what you are looking for (or close)- I wouldn't be suprised.
#2 Learn Fusion 360 basic modeling (fairly easy IMO if you already know how to design with CAD, just takes a bit more time if this is your first CAD) - there are a ton of good Fusion 360 videos out there - I'd start here (https://www.youtube.com/user/AutodeskFusion360) .
#3 Design/Model it yourself
Mounts are trypically composed of two major features - those that interface to the device, and those that interface to whatever you want to mount to (free standing on desk, car vents/dashboard,etc.). tip: It turns out that Apple has sold 1 or 2 iPad mini's so there are plenty of reference projects that have figured out the geometry for holding it (here is one). The otherside of the interface maybe where you want to prototype something /sketch and model it directly. (this is where #2 is a pre-requsite).
Just curious - are you planning to CNC machine or 3D Print the mount?
Good luck!
-Nathan
