Complex sentence: The first work which the new company published in 1808 was a piece for guitar by Antonio Nava, and this was followed in 1814 by the first catalogue, which contained 143 items.
Split into simpler sentences: The first work, which the new company published in 1808, was a guitar piece by Antonio Nava. This was followed in 1814 by the first catalogue, which contained 143 items.