Capability: the quality of being capable; practical ability it also implies possibility
it has future oriented meaning
it is the potential level of development
Ability: power to do (something physical or mental) it is your skill, expertness, talent, aptitude what you can already do
it is what we can do at present
it is the actual level of development
for example:
your capability is to lift 60kg weight. But you are not able to lift because of some problem.