Bb and C trumpets are just pitched in a different key. In general, orchestral trumpet sections that use C trumpets play with a bright projected sound, while the Bb trumpet is a darker, mellower sound. There’s also some national discrepancy; while orchestras in the USA almost always use C trumpets, in Europe (and particularly the UK), Bb trumpets are far more common. The vast majority of students begin on the Bb trumpet, as most music is written for this instrument. Once you develop, you’ll learn to transpose to be able to play on either the Bb or C trumpet as you prefer.