Reading the chromatic scale
The chromatic scale plays every half step, up and back down. This sheet spells it with flats both ways and has no key signature, so every accidental is written and lasts until the barline. Concert B♭ is the usual starting note; pick another above.
Concert pitch and your written key
Band directors name scales by concert pitch, so the whole band plays the same notes together. The trumpet is a transposing instrument: concert B♭ is written as C for you. Each scale is titled by its concert name, with your written key beside it.
Practicing scales
Use a metronome. Start slow enough to play every note clean and in tune, and speed up only once you can play the scale twice in a row without a mistake. Say or think the note names as you play, and learn the valve fingerings with them, so both are automatic by the time the scale is fast.