A Petrarchan sonnet, which is the original form of sonnet as penned by Petrarch, is written in a two-stanza form with an octave followed by a sestet, as in Petrarch's "Sonnet II." As a point of comparison, the form called English or Shakespearean sonnet varies from the Petrarchan by having three quatrains and a couplet. All sonnets comprise fourteen lines.
Petrarch's "Sonnet II" talks about Cupid's surprise attack of love arrows in a Classical allusion to the Greek god of love, Cupid. The attack is so fierce that it feels like punishment for all the love sins the speaker has committed. He laments that he has no weapons to defend himself nor uneven rising ground to hide behind to shield himself from the attack of Cupid's arrows.
The metaphor in the sonnet compares love, or what might have been called love sickness, to an ambush military attack waged by Cupid, with falling in love compared to mortal wounds in battle. The metaphor pictures the speaker as having escaped love before; as being punished for those escapes; and as defenseless against a foe. The stanzas follow the Petrarchan rhyme scheme with abbaabba in the octave (eight lines) and cdeced (a variation of the standard cdecde rhyme scheme) in the sestet (six lines).
Sometimes, the best way to understand the overt meaning of the text with a difficult poem is to write a paraphrase of, putting each line into your own words, while being very careful to attend to punctuation and look up the meanings of even familiar words that don't look like they're used quite in the right way.
Punished for a bunch of love crimes all at once,
Providing a means of vengeance for my transgressions,
Cupid took up his bow in secret,
Like someone who is a conniving coward;
My courage against love had positioned itself in my heart.
There it will defend my heart against loves who have bright eyes;
When Cupid's dread arrows are poured out against me
Hitting me where I had been weakened even before all Cupid's arrows were sent.
I was scared at the surprise attack, I found
I had neither time nor strength to repel the attack of Cupid's arrows
By using weapons suitable to fight against love arrows;
Nor had I protection from rough, rising ground.
Where can I go to speed away from defeat at Cupid's hand,
Which I want to do even now, but no method of escape do I know!