I thought a bar is 4 beats, a measure is 4 bars (in 4/4)? Going to have to look this up but is measure == phrase == section? Or I guess, a section can be arbitrary number of bars depending on song structure.

4/4 means 4 beats per bar, and we'll use a quarter note to represent a beat when writing notation. Another example would be 7/8, which is 7 beats per bar, and we'll use an eighth note for the beat when writing notation.

Looking at music in terms of bars or measures only really matters when creating traditional western sheet music notation. If we're writing computer code, or playing by ear, or looking at other kinds of music notation, those terms like "bar" and "measure" become less meaningful, and other terms become more useful or appropriate for describing the structure of the music.