The description, together with the claims, is often referred to as the specification. As this word suggests, these are the sections of the patent application where you specify what your machine or process is and how it differs from previous patents and technology.
A specification is an important part of your patent application and (later if granted) part of the legal definition of your patent. The specification must be described using clear details with full disclosures about the invention. Drawings are included in the specification when required.
* An electrical engineer would be considered an experienced person regarding electronics.