There are three basic software program types that you will need to have some knowledge of when getting ready to use your STEPCRAFT CNC system:
A design or CAD program.  Design programs like Adobe Illustrator, Inkscape, Corel Draw.  CAD programs like AutoCAD, Fusion 360, Sketchup, Solidworks, etc.  STEPCRAFT supports these and many more of the popular CAD/vector design software programs on the market.  Depending on what you are looking to do will determine how much knowledge you will need to have on a CAD or design program
A CAM (computer aided manufacturing) program. A CAM program will take the vectors or 3D model that you have designed and allow you to tell the program which tools you intent to use as well as the material size and the speeds and feed rate that you wish to run for your project.  The CAM program will output a G Code file, which is basically common machine language for CNC machines. Vectric programs like V Carve and Cut 2D make this process pretty easy.  STEPCRAFT sells and supports the full line of Vectric programs as well as Deskproto Multi-Axis CAM software.
UCCNC (or machine control software).  This program is used to setup, job and zero the STEPCRAFT CNC as well as loading and running the G Code file that was created from your CAM program.
So answer the question as to how easy it is to learn, really depends on what you are looking to do.
For example, if you are looking to do projects that are pretty complex and require that you design them in Fusion 360 or Illustrator, and you DON'T know how to use these programs, then you will have a longer learning curve since you will have to learn the design program as well.
Assuming that you already know how to use a design or CAD program, then the next program you would need to learn is a CAM program, such as Vectric V Carve.  The nice thing about V Carve (or Cut 2D) is that the interface is very easy to learn so you can be on the way of making your first CNC project in a matter of minutes.  However, as you progress, these programs have a lot of powerful features that will extend the limits on what you can create on your STEPCRAFT CNC machine.
As for UCCNC, this program takes about 15 minutes to learn how to use.  Much of what you see on the screen are buttons and features that you will not use (unless doing advanced features like automatic tool changing, etc). There are only about 5 buttons that you will need to focus on to successfully start creating projects on your STEPCRAFT right away.
This video gives you a basic overview of the software programs and how easy it is to get started right away.