Hi Jan, welcome to the EXP. Forum! Regarding your need to get set-up with CORE, I am totally with you. We're still in public Beta phase so we are constantly improving our CORE. We understand that it's still (a bit) overwhelming to new users. But bear with us, from our experience it takes at most a week to get used to
To answer your question, what is a NODE? NODE is a word we specifically chose as a container for our various business activities. We see our society as a connected network of people and resources, engaging in exchanges of goods and services. Therefore, each of our businesses / properties / projects / organizations can be registered as a Node in CORE. Within this Node, you can give it a brand name, unique slug (part of a url), assign it to a specific address, geocoordinate, time-zone, and so on. From there, you can register resources in your Node. Each resource is something that has value to someone, be that a room, a house, a bicycle, a snowboard, a skill, locla knowledge, even just ears and company.
Anyhow, I hope this helps you understand what a Node is, if you have any further questions, please do not hesitate to ask, Jan!