The difference between self a pollination and cross a pollination is:
Self- pollination occurs when the pollen from the anther is deposited on the stigma of the same flower, or another flower on the same plant.
Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of another flower on a different individual of the same species. Like bees and butterflies.
Hope this helped :)
Have a great day