Learning to read music as a singer is optional, but a small slice of notation makes new songs far faster to learn. Here is the part that pays off.
How to find the key of a song three ways: by ear from the note it rests on, from the chord symbols, or with an app, plus why the answers sometimes disagree.
Major and minor keys for singers: the single note that separates them, what each one feels like to sing, and how to hear the difference without a keyboard.
Intervals for singers explained: why they matter more than any other theory concept for pitch accuracy, with reference songs and a ten-minute daily drill.
How to read a lead sheet in plain English: the melody line, the chord symbols sitting above it, and the repeat signs and codas that tell you where to go next.
Music theory for singers, in the order it actually helps: rhythm, keys and intervals first, notation much later, and the parts you can safely ignore for good.