The Italian sonnet was mostly used by Petrarch, and it has a specific structure. It contains 14 lines, separated into one octave (a stanza of 8 lines), and one sestet (a stanza of 6 lines).
When it comes to the relation between the structure and the theme, this means that the octave introduces the idea of love within the sonnet. The poet talks about his beloved and gives us an insight into his feelings. On the other hand, the sestet analyzes his own emotions and explains in further detail why he is so infatuated with the woman (in Petrarch's case, he always wrote about Laura).
The Petrarch sonnet has an octave and a sestet. The octave would usually deal with an idea of love while in the sestet the writer would talk analyze that idea.
