Two styles of sonnets are common in the English poetry, the Petrarchan (also called Italian) sonnet and the Shakespearian (or English) sonnet. The Petrarchan sonnet, names after the Italian poet Petrarch, consist of 14 lines. It is divided into an octave (the first eight lines) and a sextet (the remaining six lines). The octave is rhymed as two quatrains, ABBA ABBA. The sextet uses two rhyme sounds, but in any order, i.e. "CDCDCD" or "CDDCDC", etc.
In terms of structure, the Petrarchan sonnet form is defined by a "turn" between the octave and sextet. This can be a shift of focus or point of view. Often, the octave poses a problem that is answered in the sextet.