I am struggling with the concept of Major Codes, Craft Codes and Tasks. Can you simplify these terms for me?

Absolutely:

CRAFT: The word “Craft” is somewhat an old English term. It refers to what we mean today as a construction trade. For example: the Framer, the Electrician, the Excavator, the Finish Carpenter, etc.

TASK: A Task is the activity performed by a Craft. As you begin to work with Tasks, think of your project schedule and the activities that you will post to it. From the examples above:

The CRAFT Performs the TASK(s):
Excavation: Excavate- The work of digging the hole in preparation for the foundation
Prep Slab-  The work of preparing the ground for the basement slab
Backfill- The work of backfilling against the outside of the foundation once it is poured
Rough Grade- The work of rough grading the lot after backfilling
Foundation: Forming, Reinforcing, Pouring & Striping the footing and foundation
Electrical: Rough Electrical
Finish Electrical
Drywall: Hanging, Taping & Texturing the drywall

The MAJOR CODE: Major Codes are simply another term for Cost Codes. They are the systems tool for organizing and collecting the costs of each Craft into its own “bucket”. For example: The Major Code “Foundation” may include all the costs of the Foundation work: the foundation labor, the reinforcing steel, the window bucks, and the concrete. In lieu of collecting all of those costs into one Major Code, you may decide to track each of those costs individually. Accordingly, you will need to establish a separate Major Code for each of those line items.