Codes Circuits and Construction is a site by Tom Igoe, Associate Arts professor at NYU, sharing code and fabrication resources for physical computing and networking.
Each section, Code, Circuits, Controllers and Communication gives the basic terminology and introduces key themes, languages, components and how to make them talk to each other.
Remember Tom Igoe has generously shared his knowledge under open source creative commons licences so you MUST provide attribution and release your modifications. It’s all released under a cc license, see the bottom of his web page.
He also recommends a number of books to help you if you get stuck and introduce you to other design areas that use physical computing and interaction.