Complex sentence: He and his friend, poet Pi Rixiu created a style of matching rhyme poetry: first one party composed a poem, the other party then reply with a new poem using the same rhyme.
Split into simpler sentences: He and his friend, the fellow poet Pi Rixiu, created a new style of matching rhyme poetry. One of them would compose a poem, and the other would then reply with a new poem using the same rhyme.