ability 为名词,能力、才能、天分的意思；指人表现出来的的实际能力,既指天赋能力,也指培养造就而获得的本领.e.g. We found him work more suited to his abilities.

able 为形容词,能够、有能力的的意思,只用于褒义；做种做事的能力.e.g. He is an able man. 他这个人很能干.常用短语为：be able to do sth.

skill 为名词,技能、技术的意思；指人经过学习掌握的技能和本领,可通过他的形容词帮助理解--skilled （有技巧的、熟练的）.e.g. He mastered a lot of skills through training and became a skilled worker in his office.