What is cytokinesis and when does it occur?

Cytokinesis is when the cytoplasm divides.
Cytokinesis occurs after and in animal cells where the cytoplasm divides. The whole process of mitosis is actually composed of many steps (Interphase, prophase, metaphase, anaphase, telophase and cytokinesis). In each step something different happens however each step is crucial to the production of a new cell.
Cytokinesis is the very last step of the mitosis process where the DNA has been successfully copied and the cell is ready to split. Cytokinesis is the point where the original cell and the newly copied cell split and their shared cytoplasm (cell fluid) is no longer shared. To simplify, its the point where you now have two seperate cells rather than one.