When notating music for trumpet there are some instrument-specific things to keep in mind.
Like tuba, cornet, tenor saxophone and clarinet, a trumpet is (usually) a transposing instrument; the note being written is different from what is sounded. A trumpetist who is asked to play a C will play a B flat... In other words, a trumpetist plays a note lower than what he/she says. In a wind band or brass band where most instruments perform thge same trick, that is not a big problem. If you want to play along with a church organ, you will have to adjust either the trumpet part (one whole tone up) or the organ part (one whole tone down).
You can convert an existing (sounding) part to trumpet in one operation with transposition C-to-B flat part.
In the score dialog with sounding parts you will see a trumpet part with transposition -2; two semitones lower than what is noted.
You can use fingering notations to specify which valves to use:
In the trill menu, the valve handles are available as 'fingering'.
When playing music, you also want to hear the trumpet. In the score dialog, select the trumpet part and select a trumpet as sounding instrument.