Explain Music Theory Basics Using Songs I Already Know

Dry theory explanations slide straight off. This one teaches scales, intervals, chords, keys and time signatures using the songs you already know by heart. You hear the concept in something familiar, so it sticks. Good if you have heard the jargon for years and never understood a word of it.

I want to understand the fundamentals of music theory, but dry explanations don't stick for me. Teach me using examples drawn from songs I already love.

Songs I know well: {FAVOURITE_SONGS}
Instrument I play (or want to): {INSTRUMENT}
Concepts I've heard of but don't understand: {MYSTERY_CONCEPTS}

Explain each of these five foundational concepts (scales, intervals, chords, keys, and time signatures) in plain English. For each one: define it in one sentence, show how it appears in one of my listed songs, and give me a 60-second experiment I can try on my instrument right now to feel the concept rather than just read about it.