It's easy if you use a piano or the piano staff at the top of the program.

You pick a note for the guitar, that what you play. Then you count up two keys on the piano.

So looking at it as C go to the black key as one (C# or Db) and then then next one which is a D. So that's 2 semi tones.

The trumpet is always going to read higher on the register, unless you go down and then you go up 2 like before and transpose down a whole octave.

Try it with numerous keys and play scales together.

Or the guitar with chords and the trumpet with notes.

John Conley
Musica est vita