Can someone please explain how/why they're generated?
You have a double stranded DNA molecule. One end is the 5' end, and the antiparallel end is the 3' end. So DNA helicase moves along the DNA helix and simultaneously unwinds the DNA, whilst this is happening, RNA polymerase synthesises primers on both DNA template strands. When the primers are added onto the DNA templates, we know that DNA polymerase can attach to them and begin synthesising the daughter strands. DNA polymerase only works in the 5'-3' direction, so it only synthesises DNA in the 5 prime to 3 prime direction. As DNA helicase moves along the DNA, one of the template strands also runs in the direction of the helicase in the 3'-5' direction, so this will be continuously synthesised. However, as the antiparallel orientation of DNA, the opposite strand will run in the 5'-3' direction, so as DNA helicase unwinds the DNA helix, the 3' ends keep getting exposed as it moves along. So as they keep getting exposed, new primers are attached to those sections and DNA polymerase starts to synthesise the daughter strand (lagging strand) creating fragments, known as Okazaki fragments. These fragments are then bonded together via DNA ligase, which forms phosphodiester bonds between the backbones of the fragments.