CS50 on YouTube · Open on YouTube
Foundations: programming and problem solving · Novice · Lesson 7 of 98 · 2 h 1 min video, then about 5 hours of practice
How computers represent data and run programs
After this you can explain what a program, a variable, a loop and a function are at the level of how a computer actually executes them.
Why it matters
Starting here, rather than with a language's syntax, saves you months of confusion later. Bits, binary, how text and images become numbers, and what an algorithm is: these ideas make every later abstraction less magical. CS50's first lecture is the best free introduction to computational thinking anywhere. It uses Scratch, a visual language, so that you learn the ideas (conditions, loops, functions, variables) without fighting syntax. Trap: do not skip this because it 'looks like a kids' tool'. The concepts are exactly the ones you need, and the lecture is aimed at adults.
How to use this resource
Watch the whole lecture. Then build one small Scratch program of your own before moving on.