First you need to open 360 Fusion and make sure you have the latest version. On the upper left, click Fusion 360 --> About Fusion 360. Version 2.0.7046 is the latest for Mac. If it's not updated, check the clock icon (job status) in the upper right. It will have a "1" on it if updating is needed. Close Fusion.
Now go to the fusion 360 App store. Find "Slicer" app. Click and download for Mac or Windows. Install. Then open Fusion. When in the "Design Workspace," click the Tools tab. Under Make, you should now see Slicer available. More on this later.
In 360 Fusion, draw the 3D model of your mascot at the actual scale you hope to build it. The rough size we are going for is that it fits within a 25 cm cube. If you have a long skinny mascot, you may lengthen one dimension, by shortening the other two. Use 360 Fusion to make the rough shape of the major parts of your mascot. In general, don't try to make small parts such as teeth, fingers, eyeballs, etc. The screen shot on this page of penguin body is a nice example of what a rough body form could look like.
Here's some helpful vids for Mascot creation.
Here is a screen shot from 360 Fusion of my penguin body. I made the head and body separately (as forms) with the sculpting environment.
Here is an example of how I turned the 3D image into cardboard slices using the Slicer program. This is one of two sheets that I cut out on the Epilogue Laser, and then held together with glue and two dowel rods.