Complex sentence: When the owner of a tin business, John Wilson, saw him with his cart, he began giving him copper trimmings which were of no use, and Mayer considered Wilson to be his first partner and his best friend.
Split into simpler sentences: When the owner of a tin business, John Wilson, saw him with his cart, he began giving him copper trimmings which were of no use. He considered Wilson to be his first partner and his best friend.