Simplistic term Answer - Difference between Asexual and Sexual is
Asexual does not need a mate. For example a hydra or a star fish which they can split their body and self regenerate into both halves with two star fish full regenerated.
Sexual has to have either an internal fert. or external fert. with a needed partner. Just like us humans a female reproductives and males sperm to create a another scary living.