The treble staff
Written music sits on five lines. A note is either ON a line or IN the space between two of them, and that position is the whole message: it says which key to play.
Move up one position — line, space, line — and you move up one letter. The bottom line is E, the space above it F, the next line G, and so on up the alphabet.
The curly sign at the front is the treble clef. It marks the lines that carry the notes you play with your right hand. Middle C sits just below this staff, on a short line of its own.
Reading and naming are two skills, so both are practised here: find the written key, and say the note's name. The lines from the bottom are E, G, B, D, F; the four spaces spell FACE.
one position up = one letter up
Middle C on its short line, then E on the bottom line, G, and B.
Practise this in the trainer — it opens with this lesson the first time the concept comes up.