Use the clef as your anchor
A staff has five lines and four spaces. Count both from the bottom. The treble clef curls around the second line, which represents G. From that G, one step upward to the next space is A; the next line is B. The sequence continues C, D, E, F, G, and starts again.
The five line notes, bottom to top, are E, G, B, D, F. The four space notes are F, A, C, E. A mnemonic can help, but learning nearby notes from a reference pitch also helps you read without reciting an entire list.
Continue beyond the staff
Ledger lines are short extra lines for notes too high or low for the main staff. The pattern does not change. Immediately below the bottom E line is a space D; the first ledger line below is C. Continue downward with B in the next space and A on the next ledger line.
For guitar, remember that these are written pitches. The low open E string sounds E2 and is written E3, below the staff. Work out the line or space first, then use the app to check the note and guitar position.
Try it yourself
What note is in the space just above the second line?
Show the answer
A (la). The second line is G, and the next staff step upward is A.