First drill: this is the base upon which the syllabus is built.
The drill begins with the first pairing of guards we see in the 12 guards section of the MS: tutta porta di ferro and donna destra (though forward weighted). Donna attacks with a mandritto fendente. TPDF parries, achieves the crossing of the second master of the zogho largo, at the middle of the swords. The parry beats the attack wide, and the defender strikes over the arm and into the chest (2nd play, which "completes the play" of the 2nd master). Attacker counters this with an application of the lesson of the 8th play of the sword on horseback; defender counters that with an application of the lesson of the ninth.
All other drills can be concieved of as variations on this one: Second drill has the defender start a different guard (dente di zenghiaro); the Exchange of thrust defends against a different attack, the Breaking the thrust is a variation on that, demanded by the attacker's change of side.
The Four crossings drill gives four possible crossings, and acts as a multiplier on the basic four drills: the basic form of them are all exemplars of the first crossing: the sword is beaten wide. The Woman in the Window drill for example, includes the Breaking the thrust and the feint, which can be thought of as the point remaining in presence after the crossing has been attempted, so an application of the second crossing.
Ken Quek and GW demonstrating.