Complex sentence: They explain their origins to the two humans and insist on the urgency to get to the Allspark first before the Decepticons, knowing that the Decepticons plan to use it to turn all of Earth's technologies into a new army of Transformers and render humanity extinct.
Split into simpler sentences: They explain their origins to the two humans and insist on the urgency to get to the Allspark first before the Decepticons. Otherwise, the Decepticons would use the Allspark to turn all of Earth's technologies into a new army of Transformers and render humanity extinct.