I'm only playing simple pieces (Grade 1 in the UK) but even some of these have Tr notation next to a note, and a separate bit of score above the score.
What I notice is, the note in the main score is nothing like the notes shown in the trill pattern. e.g:
How should the trill "mini-score" be read? It's optional in my pieces but I'd at least like to know what it means.
By the way this is in the key of G-major, so F->F#.